Scanning CL_TYPE_MSEXE that have embedded file type signature matches
for CL_TYPE_MSEXE are incorrectly passing the PE header check for the
contained file, resulting in excessive scan times.
The problem is that the `peinfo` struct needs to have the `offset` set
for the contained `CL_TYPE_MSEXE` match prior to the header check.
Without that, the header check was actually validating the PE header of
the original file, which would always pass when that's a PE, and would
always fail if it's an OLE2 file (the other type which we check for
contained PEs).
The additional code change in this commit is to make it so the `ctx`
parameter must never be NULL, and removing the `map` parameter because,
in practice, that is always from `ctx->fmap`. This is to safeguard
against future changes to the function that may accidentally use `ctx`
without a proper NULL check.
CLAM-2882
When embedded file type recognition finds a possible embedded file, it
is being scanned as a new embedded file even if it turns out it was a
false positive and parsing fails. My solution is to pre-parse the file
headers as little possible to determine if it is valid. If possible,
also determine the file size based on the headers. That will make it so
we don't have to scan additional data when the embedded file is not at
the very end.
This commit adds header checks prior to embedded ZIP, ARJ, and CAB
scanning. For these types I was also able to use the header checks to
determine the object size so as to prevent excessive pattern matching.
TODO: Add the same for RAR, EGG, 7Z, NULSFT, AUTOIT, IShield, and PDF.
This commit also removes duplicate matching for embedded MSEXE.
The embedded MSEXE detection and scanning logic was accidentally
creating an extra duplicate layer in between scanning and detection
because of the logic within the `cli_scanembpe()` function.
That function was effectively doing the header check which this commit
adds for ZIP, ARJ, and CAB but minus the size check.
Note: It is unfortunately not possible to get an accurage size from PE
file headers.
The `cli_scanembpe()` function also used to dump to a temp file for no
reason since FMAPs were extended to support windows into other FMAPs.
So this commit removes the intermediate layer as well as dropping a temp
file for each embedded PE file.
Further, this commit adds configuration and DCONF safeguards around all
embedded file type scanning.
Finally, this commit adds a set of tests to validate proper extraction
of embedded ZIP, ARJ, CAB, and MSEXE files.
CLAM-2862
Co-authored-by: TheRaynMan <draynor@sourcefire.com>
We presently record Alerts as an array of signature names.
Instead, it should be an object with properties of its own.
We should record alerting indicators and weak indicators in a single
"Indicators", likely with the same structure as the "Alerts" objects.
When an alerting indicator is ignored (e.g. ignored by callback or if
the file is trusted by an FP signature), we can remove it from the
"Alerts" array, and for the "Indicators" array, add a "Ignored" key with
a string value that explains why it was ignored.
This eliminates the need to track and propagate the additional
"WeakIndicators" and "IgnoredAlerts" arrays.
It is a shortcoming of existing scan APIs that it is not possible
to return an error without masking a verdict.
We presently work around this limitation by counting up detections at
the end and then overriding the error code with `CL_VIRUS`, if necessary.
The `cl_scanfile_ex()`, `cl_scandesc_ex()`, and `cl_scanmap_ex()` functions
should provide the scan verdict separately from the error code.
This introduces a new enum for recording and reporting a verdict:
`cl_verdict_t` with options:
- `CL_VERDICT_NOTHING_FOUND`
- `CL_VERDICT_TRUSTED`
- `CL_VERDICT_STRONG_INDICATOR`
- `CL_VERDICT_POTENTIALLY_UNWANTED`
Notably, the newer scan APIs may set the verdict to `CL_VERDICT_TRUSTED`
if there is a (hash-based) FP signature for a file, or in the cause where
Authenticode or similar certificate-based verification was performed, or
in the case where an application scan callback returned `CL_VERIFIED`.
CLAM-763
CLAM-865
Temp directory recursion in ClamAV is when each layer of a scan gets its
own temp directory in the parent layer's temp directory.
In addition to temp directory recursion, ClamAV has been creating a new
subdirectory for each file scan as a risk-adverse method to ensure
no temporary file leaks fill up the disk.
Creating a directory is relatively slow on Windows in particular if
scanning a lot of very small files.
This commit:
1. Separates the temp directory recursion feature from the leave-temps
feature so that libclamav can leave temp files without making
subdirectories for each file scanned.
2. Makes it so that when temp directory recursion is off, libclamav
will just use the configure temp directory for all files.
The new option to enable temp directory recursion is for libclamav-only
at this time. It is off by default, and you can enable it like this:
```c
cl_engine_set_num(engine, CL_ENGINE_TMPDIR_RECURSION, 1);
```
For the `clamscan` and `clamd` programs, temp directory recursion will
be enabled when `--leave-temps` / `LeaveTemporaryFiles` is enabled.
The difference is that when disabled, it will return to using the
configured temp directory without making a subdirectory for each file
scanned, so as to improve scan performance for small files, mostly on
Windows.
Under the hood, this commit also:
1. Cleans up how we keep track of tmpdirs for each layer.
The goal here is to align how we keep track of layer-specific stuff
using the scan_layer structure.
2. Cleans up how we record metadata JSON for embedded files.
Note: Embedded files being different from Contained files, as they
are extracted not with a parser, but by finding them with
file type magic signatures.
CLAM-1583
Move recording of evidence (aka Strong, PUA, and Weak indicators) to be
done in each layer of a scan, and passed up to the parent layer with the
top level only connecting the results at the very end of the scan.
This is needed to provide access the last alert for a given layer when
we upgrade the scan callbacks.
Note that when adding evidence from a child layer that is a normalized
layer, we do not want to increase the depth. It should appear as though
the match occured on the parent layer.
This is for two reasons:
1. We don't run the scan callbacks on normalized layers.
2. Future matches on Weak Indicators should be able to treat normalized
layer matches the same as original file matches. Keep reading for
more about Weak Indicators.
Recording scan matches at each recursion layer is also needed to support
Weak Indicators, a feature where an alerting signature (aka Strong
Indicator) may require the the match of a non-alerting signature (aka
Weak Indicator) on the same layer or on child layers in order to alert.
Support for Weak indicators was blocked by not keeping track of where
indicators were found. So this commit also enables support for recording
Weak indicators.
Like PUA, Weak indicators are treated differently based on the signature
prefix. That is, any signatures starting with "Weak." won't cause an
alert on its own.
The next step to completing Weak Indicator support will be adding a
logical subsignature feature to depend on a weak indicator match.
CLAM-2626
CLAM-2485
Every time we push a new map onto the scanning recursion context, give
it a unique object id number, which counts from zero.
Moved the location where we add metadata for each file from the
"cli_magic_scan" function over to the "recursion stack push" function.
Include a "path" as a parameter for creating a new fmap, and rename some
related variables and functions to be more intuitive.
CLAM-2796
See also: CLAM-2485, CLAM-2626
Change the clean-cache to use SHA2-256 instead of MD5.
Note that all references are changed to specify "SHA2-256" now instead
of "SHA256", for clarity. But there is no plan to add support for SHA3
algorithms at this time.
Significant code cleanup. E.g.:
- Implemented goto-done error handling.
- Used `uint8_t *` instead of `unsigned char *`.
- Use `bool` for boolean checks, rather than `int.
- Used `#defines` instead of magic numbers.
- Removed duplicate `#defines` for things like hash length.
Add new option to calculate and record additional hash types when the
"generate metadata JSON" feature is enabled:
- libclamav option: `CL_SCAN_GENERAL_STORE_EXTRA_HASHES`
- clamscan option: `--json-store-extra-hashes` (default off)
- clamd.conf option: `JsonStoreExtraHashes` (default 'no')
Renamed the sigtool option `--sha256` to `--sha2-256`.
The original option is still functional, but is deprecated.
For the "generate metadata JSON" feature, the file hash is now stored as
"sha2-256" instead of "FileMD5". If you enable the "extra hashes" option,
then it will also record "md5" and "sha1".
Deprecate and disable the internal "SHA collect" feature.
This option had been hidden behind C #ifdef checks for an option that
wasn't exposed through CMake, so it was basically unavailable anyways.
Changes to calculate file hashes when they're needed and no sooner.
For the FP feature in the matcher module, I have mimiced the
optimization in the FMAP scan routine which makes it so that it can
calculate multiple hashes in a single pass of the file.
The `HandlerType` feature stores a hash of the file in the scan ctx to
prevent retyping the exact same data more than once.
I removed that hash field and replaced it with an attribute flag that is
applied to the new recursion stack layer when retyping a file.
This also closes a minor bug that would prevent retyping a file with an
all-zero hash. :)
The work upgrading cache.c to support SHA2-256 sized hashes thanks to:
https://github.com/m-sola
CLAM-255
CLAM-1858
CLAM-1859
CLAM-1860
As of ClamAV 0.105, libjson-c is required.
There is also no option to disable libjson-c support.
This commit removes the dead code associated with the old build
option.
We add the _OR_GOTO_DONE suffix to the macros that go to done if the
allocation fails. This makes it obvious what is different about the
macro versus the equivalent function, and that error handling is
built-in.
Renamed the cli_strdup to safer_strdup to make it obvious that it exists
because it is safer than regular strdup. Regular strdup doesn't have the
NULL check before trying to dup, and so may result in a NULL-deref
crash.
Also remove unused STRDUP (_OR_GOTO_DONE) macro, since the one with the
NULL-check is preferred.
The cli_max_malloc, cli_max_calloc, and cli_max_realloc functions
provide a way to protect against allocating too much memory
when the size of the allocation is derived from the untrusted input.
Specifically, we worry about values in the file being scanned being
manipulated to exhaust the RAM and crash the application.
There is no need to check the limits if the size of the allocation
is fixed, or if the size of the allocation is necessary for signature
loading, or the general operation of the applications.
E.g. checking the max-allocation limit for the size of a hash, or
for the size of the scan recursion stack, is a complete waste of
time.
Although we significantly increased the max-allocation limit in
a recent release, it is best not to check an allocation if the
allocation will be safe. It would be a waste of time.
I am also hopeful that if we can reduce the number allocations
that require a limit-check to those that require it for the safe
scan of a file, then eventually we can store the limit in the scan-
context, and make it configurable.
We have some special functions to wrap malloc, calloc, and realloc to
make sure we don't allocate more than some limit, similar to the
max-filesize and max-scansize limits. Our wrappers are really only
needed when allocating memory for scans based on untrusted user input,
where a scan file could have bytes that claim you need to allocate
some ridiculous amount of memory. Right now they're named:
- cli_malloc
- cli_calloc
- cli_realloc
- cli_realloc2
... and these names do not convey their purpose
This commit renames them to:
- cli_max_malloc
- cli_max_calloc
- cli_max_realloc
- cli_max_realloc2
The realloc ones also have an additional feature in that they will not
free your pointer if you try to realloc to 0 bytes. Freeing the memory
is undefined by the C spec, and only done with some realloc
implementations, so this stabilizes on the behavior of not doing that,
which should prevent accidental double-free's.
So for the case where you may want to realloc and do not need to have a
maximum, this commit adds the following functions:
- cli_safer_realloc
- cli_safer_realloc2
These are used for the MPOOL_REALLOC and MPOOL_REALLOC2 macros when
MPOOL is disabled (e.g. because mmap-support is not found), so as to
match the behavior in the mpool_realloc/2 functions that do not make use
of the allocation-limit.
There are a large number of allocations for fix sized buffers using the
`cli_malloc` and `cli_calloc` calls that check if the requested size is
larger than our allocation threshold for allocations based on untrusted
input. These allocations will *always* be higher than the threshold, so
the extra stack frame and check for these calls is a waste of CPU.
This commit replaces needless calls with A -> B:
- cli_malloc -> malloc
- cli_calloc -> calloc
- CLI_MALLOC -> MALLOC
- CLI_CALLOC -> CALLOC
I also noticed that our MPOOL_MALLOC / MPOOL_CALLOC are not limited by
the max-allocation threshold, when MMAP is found/enabled. But the
alternative was set to cli_malloc / cli_calloc when disabled. I changed
those as well.
I didn't change the cli_realloc/2 calls because our version of realloc
not only implements a threshold but also stabilizes the undefined
behavior in realloc to protect against accidental double-free's.
It may be worth implementing a cli_realloc that doesn't have the
threshold built-in, however, so as to allow reallocaitons for things
like buffers for loading signatures, which aren't subject to the same
concern as allocations for scanning possible malware.
There was one case in mbox.c where I changed MALLOC -> CLI_MALLOC,
because it appears to be allocating based on untrusted input.
Coverity is unhappy with the use of the EC32, cli_readint32,
and cli_writeint32 macros (and the 64bit equivalents to potentially
change the endianess of variables in place.
It claims:
overlapping_assignment: Assigning ... to ..., which have overlapping
memory locations and different types.
Using a temporary variable in between reading and writing should
resolve these "high impact" complaints.
Resolves: Coverity-225232. 225225, 225215, 225212, 225180, 225170,
225165, 225161, 225159.
A few user of VirtualAddress and Size in cli_exe_info::pe_image_data_dir
don't use the endian wrapper while other places do. This leads to
testsuite failures on big endian machines.
Convert the content of struct pe_image_data_dir to native format so that
that the EC32() conversation can be removed.
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
The header parsing / executable metadata collecting functions for the
PE, ELF, and Mach-O file types were using `int` for the return type.
Mostly they were returning 0 for success and -1, -2, -3, or -4 for
failure. But in some cases they were returning cl_error_t enum values
for failure. Regardless, the function using them was treating 0 as
success and non-zero as failure, which it stored as -1 ... every time.
This commit switches them all to use cl_error_t. I am continuing to
storeo the final result as 0 / -1 in the `peinfo` struct, but outside of
that everything has been made consistent.
While I was working on that, I got a tad side tracked. I noticed that
the target type isn't an enum, or even a set of #defines. So I made an
enum and then changed the code that uses target types to use the enum.
I also removed the `target` parameter from a number of functions that
don't actually use it at all. Some recursion was masking the fact that
it was an unused parameter which is why there was no warning about it.
Signatures that start with "PUA.", "Heuristics.", or "BC.Heuristics."
are perceived to be less serious, or more likely to have false
positives, than other signatures that we would think of us as "strong
indicators".
At present, only a subset of "Heuristics." signatures, such as those
added by the phishing module, are added as "potentially unwanted".
Unless you're using heuristic-precedence mode, these "potentially
unwanted" indicators are recorded but not reported unless no other
signature alerts. This behavior should apply to all signatures that
start with "PUA." and "Heuristics.". We already do a string match
comparison on the signature name to apply that behavior to bytecode
matches that start with "BC.Heuristics.".
I moved that string comparison logic used for "BC.Heuristics." into the
main `cl_append_virus()` function and extended it to cover the other two
cases.
I also replaced all hardcoded calls to append "Heuristics." signatures
to append using the `cli_append_potentially_unwanted()` function, so we
can skip the string compare in these cases. That function will of course
append them as strong indicators if heuristic-precedence mode is
enabled.
Significantly tidy the `cli_scan_fmap()` function, and add comments to
explain how it all works.
Add SHA1 and SHA256 digest variables to the FMAP structure in addition
to the existing MD5. Add a function to set the hash so that when we
calculate the hashes for hash matching, we save them for subsequent FP
matching. This enabled me to remove the extra "hash-only" FP check from
`cli_scan_fmap()`. This will also make it easier to switch the clean
cache hash algorithm to SHA256 in the future.
Remove extra allmatch checks that are no longer required.
Add a new header to prevent #include order issues.
Rework the append_virus mechanism to store evidence (strong indicators,
pua indicators, and eventually weak indicators) in vectors. When
appending a "virus", we will return CLEAN when in allmatch-mode, and
simply add the indicator to the appropriate vector.
Later we can check if there were any alerts to return a vector by
summing the lengths of the strong and pua indicator vectors.
This does away with storing the latest "virname" in the scan context.
Instead, we can query for the last indicator in the evidence, giving
priority to strong indicators.
When heuristic-precendence is enabled, add PUA as Strong instead of
as PotentiallyUnwanted. This way, they will be treated equally and
reported in order in allmatch mode.
Also document reason for disabling cache with metadata JSON enabled
The current implementation sets a "next layer attributes" flag field
in the scan context. This may introduce bugs if accidentally not cleared
during error handling, causing that attribute to be applied to a
different layer than intended.
This commit resolves that by adding an attribute flag to the major
internal scan functions and removing the "next layer attributes" from
the scan context. This attributes flag shares the same flag fields as
the attributes flag in the new file inspection callback and the flags
are defined in `clamav.h`.
In the PE parser when reading up to 4KB following the entrypoint
there's is no call to verify if the read failed. Later it is assumed
that the read succeeded and that the data in the buffer is valid.
I believe the correct response is to bail out if the read failed.
I also fixed some warnings:
- The the max # of PE sections was effectively disabled by setting it
to the max size of a uint16_t, so the max-check was pointless.
- Some undocumented switch fall-throughs were throwing warnings as well.
- Unsigned integer subtraction results in a signed value, which was
throwing warnings when compared with another unsigned value. The
substraction for `peinfo->nsections - 1` won't be less than 0 though
because we've already verified that nsections != 0 so we can just cast
the result of the subtraction back to an unsigned value to silence the
warning safely.
Commit f82492aef4 fixed a crash in Windows
debug builds but in so doing accidentally introduced a possible crash
when scanning PE files that lack import tables. The issue being that
the openssl hashing functions try to "finish" a hash that was never
started.
This commit fixes the issue by returning CL_BREAK instead of CL_SUCCESS
when the import table doesn't exist or RVA is invalid so that we can
differentiate between successfully calculating the hashes and
successfully skipping the hashing process.
The endianness conversion when reading the PE image import descriptor is
making the change in-place in the fmap.
On Windows, the fmap is read-only and so in Debug builds that's causing
a crash.
This uses a buffer on the stack and copies each image import descriptor
before doing the conversions and then processing each.
* Added loglevel parameter to logg()
* Fix logg and mprintf internals with new loglevels
* Update all logg calls to set loglevel
* Update all mprintf calls to set loglevel
* Fix hidden logg calls
* Executed clam-format
The PE section hash scanning code didn't implement the all-match check.
While this check isn't the ideal implementation for all-match mode...
(see the commit message for the previous commit)
...it's simple enough to add the all-match check here for now.
The fixes to the fmap bounds for nested (duplicate) fmaps added recently
introduced a subtle arithmetic bug that was detected by OSS-Fuzz:
```c
scanat = m->nested_offset + *at % m->pgsz;
```
should have been:
```c
scanat = (m->nested_offset + *at) % m->pgsz;
```
Without the parenthesis, `scanat` could be > `m->pgsz`, which would
overflow in the subsequent `memchr()` call.
See:
- https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=40452
- https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=40455
This commit also tightens up some of the other bounds checks done with
`CLI_ISCONTAINED()` macro so the check limits the bounds to the nested
fmap and not the original map.
In addition, I've added a `CLI_ISCONTAINED_0_TO()` macro that removes
checks when the "bigger" buffer starts at offset 0. This should silence
a bunch of (benign) warnings and medium severity Coverity issues.
There is also a possible use of an uninitialized variable
(`old_hook_lsig_matches`) in `cli_magic_scan()`.
Finally, I also removed an unecessary NULL-check on `filebase` in
`fmap_dup_to_file()` that Coverity was unhappy with.
Scan recursion is the process of identifying files embedded in other
files and then scanning them, recursively.
Internally this process is more complex than it may sound because a file
may have multiple layers of types before finding a new "file".
At present we treat the recursion count in the scanning context as an
index into both our fmap list AND our container list. These two lists
are conceptually a part of the same thing and should be unified.
But what's concerning is that the "recursion level" isn't actually
incremented or decremented at the same time that we add a layer to the
fmap or container lists but instead is more touchy-feely, increasing
when we find a new "file".
To account for this shadiness, the size of the fmap and container lists
has always been a little longer than our "max scan recursion" limit so
we don't accidentally overflow the fmap or container arrays (!).
I've implemented a single recursion-stack as an array, similar to before,
which includes a pointer to each fmap at each layer, along with the size
and type. Push and pop functions add and remove layers whenever a new
fmap is added. A boolean argument when pushing indicates if the new layer
represents a new buffer or new file (descriptor). A new buffer will reset
the "nested fmap level" (described below).
This commit also provides a solution for an issue where we detect
embedded files more than once during scan recursion.
For illustration, imagine a tarball named foo.tar.gz with this structure:
| description | type | rec level | nested fmap level |
| ------------------------- | ----- | --------- | ----------------- |
| foo.tar.gz | GZ | 0 | 0 |
| └── foo.tar | TAR | 1 | 0 |
| ├── bar.zip | ZIP | 2 | 1 |
| │  └── hola.txt | ASCII | 3 | 0 |
| └── baz.exe | PE | 2 | 1 |
But suppose baz.exe embeds a ZIP archive and a 7Z archive, like this:
| description | type | rec level | nested fmap level |
| ------------------------- | ----- | --------- | ----------------- |
| baz.exe | PE | 0 | 0 |
| ├── sfx.zip | ZIP | 1 | 1 |
| │  └── hello.txt | ASCII | 2 | 0 |
| └── sfx.7z | 7Z | 1 | 1 |
|   └── world.txt | ASCII | 2 | 0 |
(A) If we scan for embedded files at any layer, we may detect:
| description | type | rec level | nested fmap level |
| ------------------------- | ----- | --------- | ----------------- |
| foo.tar.gz | GZ | 0 | 0 |
| ├── foo.tar | TAR | 1 | 0 |
| │ ├── bar.zip | ZIP | 2 | 1 |
| │ │  └── hola.txt | ASCII | 3 | 0 |
| │ ├── baz.exe | PE | 2 | 1 |
| │ │ ├── sfx.zip | ZIP | 3 | 1 |
| │ │ │  └── hello.txt | ASCII | 4 | 0 |
| │ │ └── sfx.7z | 7Z | 3 | 1 |
| │ │   └── world.txt | ASCII | 4 | 0 |
| │ ├── sfx.zip | ZIP | 2 | 1 |
| │ │  └── hello.txt | ASCII | 3 | 0 |
| │ └── sfx.7z | 7Z | 2 | 1 |
| │  └── world.txt | ASCII | 3 | 0 |
| ├── sfx.zip | ZIP | 1 | 1 |
| └── sfx.7z | 7Z | 1 | 1 |
(A) is bad because it scans content more than once.
Note that for the GZ layer, it may detect the ZIP and 7Z if the
signature hits on the compressed data, which it might, though
extracting the ZIP and 7Z will likely fail.
The reason the above doesn't happen now is that we restrict embedded
type scans for a bunch of archive formats to include GZ and TAR.
(B) If we scan for embedded files at the foo.tar layer, we may detect:
| description | type | rec level | nested fmap level |
| ------------------------- | ----- | --------- | ----------------- |
| foo.tar.gz | GZ | 0 | 0 |
| └── foo.tar | TAR | 1 | 0 |
| ├── bar.zip | ZIP | 2 | 1 |
| │  └── hola.txt | ASCII | 3 | 0 |
| ├── baz.exe | PE | 2 | 1 |
| ├── sfx.zip | ZIP | 2 | 1 |
| │  └── hello.txt | ASCII | 3 | 0 |
| └── sfx.7z | 7Z | 2 | 1 |
|   └── world.txt | ASCII | 3 | 0 |
(B) is almost right. But we can achieve it easily enough only scanning for
embedded content in the current fmap when the "nested fmap level" is 0.
The upside is that it should safely detect all embedded content, even if
it may think the sfz.zip and sfx.7z are in foo.tar instead of in baz.exe.
The biggest risk I can think of affects ZIPs. SFXZIP detection
is identical to ZIP detection, which is why we don't allow SFXZIP to be
detected if insize of a ZIP. If we only allow embedded type scanning at
fmap-layer 0 in each buffer, this will fail to detect the embedded ZIP
if the bar.exe was not compressed in foo.zip and if non-compressed files
extracted from ZIPs aren't extracted as new buffers:
| description | type | rec level | nested fmap level |
| ------------------------- | ----- | --------- | ----------------- |
| foo.zip | ZIP | 0 | 0 |
| └── bar.exe | PE | 1 | 1 |
| └── sfx.zip | ZIP | 2 | 2 |
Provided that we ensure all files extracted from zips are scanned in
new buffers, option (B) should be safe.
(C) If we scan for embedded files at the baz.exe layer, we may detect:
| description | type | rec level | nested fmap level |
| ------------------------- | ----- | --------- | ----------------- |
| foo.tar.gz | GZ | 0 | 0 |
| └── foo.tar | TAR | 1 | 0 |
| ├── bar.zip | ZIP | 2 | 1 |
| │  └── hola.txt | ASCII | 3 | 0 |
| └── baz.exe | PE | 2 | 1 |
| ├── sfx.zip | ZIP | 3 | 1 |
| │  └── hello.txt | ASCII | 4 | 0 |
| └── sfx.7z | 7Z | 3 | 1 |
|   └── world.txt | ASCII | 4 | 0 |
(C) is right. But it's harder to achieve. For this example we can get it by
restricting 7ZSFX and ZIPSFX detection only when scanning an executable.
But that may mean losing detection of archives embedded elsewhere.
And we'd have to identify allowable container types for each possible
embedded type, which would be very difficult.
So this commit aims to solve the issue the (B)-way.
Note that in all situations, we still have to scan with file typing
enabled to determine if we need to reassign the current file type, such
as re-identifying a Bzip2 archive as a DMG that happens to be Bzip2-
compressed. Detection of DMG and a handful of other types rely on
finding data partway through or near the ned of a file before
reassigning the entire file as the new type.
Other fixes and considerations in this commit:
- The utf16 HTML parser has weak error handling, particularly with respect
to creating a nested fmap for scanning the ascii decoded file.
This commit cleans up the error handling and wraps the nested scan with
the recursion-stack push()/pop() for correct recursion tracking.
Before this commit, each container layer had a flag to indicate if the
container layer is valid.
We need something similar so that the cli_recursion_stack_get_*()
functions ignore normalized layers. Details...
Imagine an LDB signature for HTML content that specifies a ZIP
container. If the signature actually alerts on the normalized HTML and
you don't ignore normalized layers for the container check, it will
appear as though the alert is in an HTML container rather than a ZIP
container.
This commit accomplishes this with a boolean you set in the scan context
before scanning a new layer. Then when the new fmap is created, it will
use that flag to set similar flag for the layer. The context flag is
reset those that anything after this doesn't have that flag.
The flag allows the new recursion_stack_get() function to ignore
normalized layers when iterating the stack to return a layer at a
requested index, negative or positive.
Scanning normalized extracted/normalized javascript and VBA should also
use the 'layer is normalized' flag.
- This commit also fixes Heuristic.Broken.Executable alert for ELF files
to make sure that:
A) these only alert if cli_append_virus() returns CL_VIRUS (aka it
respects the FP check).
B) all broken-executable alerts for ELF only happen if the
SCAN_HEURISTIC_BROKEN option is enabled.
- This commit also cleans up the error handling in cli_magic_scan_dir().
This was needed so we could correctly apply the layer-is-normalized-flag
to all VBA macros extracted to a directory when scanning the directory.
- Also fix an issue where exceeding scan maximums wouldn't cause embedded
file detection scans to abort. Granted we don't actually want to abort
if max filesize or max recursion depth are exceeded... only if max
scansize, max files, and max scantime are exceeded.
Add 'abort_scan' flag to scan context, to protect against depending on
correct error propagation for fatal conditions. Instead, setting this
flag in the scan context should guarantee that a fatal condition deep in
scan recursion isn't lost which result in more stuff being scanned
instead of aborting. This shouldn't be necessary, but some status codes
like CL_ETIMEOUT never used to be fatal and it's easier to do this than
to verify every parser only returns CL_ETIMEOUT and other "fatal
status codes" in fatal conditions.
- Remove duplicate is_tar() prototype from filestypes.c and include
is_tar.h instead.
- Presently we create the fmap hash when creating the fmap.
This wastes a bit of CPU if the hash is never needed.
Now that we're creating fmap's for all embedded files discovered with
file type recognition scans, this is a much more frequent occurence and
really slows things down.
This commit fixes the issue by only creating fmap hashes as needed.
This should not only resolve the perfomance impact of creating fmap's
for all embedded files, but also should improve performance in general.
- Add allmatch check to the zip parser after the central-header meta
match. That way we don't multiple alerts with the same match except in
allmatch mode. Clean up error handling in the zip parser a tiny bit.
- Fixes to ensure that the scan limits such as scansize, filesize,
recursion depth, # of embedded files, and scantime are always reported
if AlertExceedsMax (--alert-exceeds-max) is enabled.
- Fixed an issue where non-fatal alerts for exceeding scan maximums may
mask signature matches later on. I changed it so these alerts use the
"possibly unwanted" alert-type and thus only alert if no other alerts
were found or if all-match or heuristic-precedence are enabled.
- Added the "Heuristics.Limits.Exceeded.*" events to the JSON metadata
when the --gen-json feature is enabled. These will show up once under
"ParseErrors" the first time a limit is exceeded. In the present
implementation, only one limits-exceeded events will be added, so as to
prevent a malicious or malformed sample from filling the JSON buffer
with millions of events and using a tonne of RAM.
docs: Fix a few typos
There are small typos in:
- libclamav/others_common.c
- libclamav/pe.c
- libclamav/unzip.c
Fixes:
- Should read `descriptor` rather than `desriptor`.
- Should read `record` rather than `reocrd`.
- Should read `overarching` rather than `overaching`.
Trusted SHA256-based Authenticode hashes can now be loaded in
from .cat files. In addition:
- Files that are covered by Authenticode hashes loaded in from
.cat files will now be treated as VERIFIED like executables
where the embedded Authenticode sig is deemed to be trusted
based on .crb rules. This fixes a regression introduced in
0.102 (I think).
- The Authenticode hashes for signed EXEs without .crb coverage
will no longer be computed in cli_check_auth_header unless
hashes from .cat rules have been loaded. This fixes a slight
performance regression introduced in 0.102 (I think).
Windows XP had a maximum section count of 96, and this has been
the max for ClamAV forever as well. Raising this prevents malicious
executables from being able to evade certain ClamAV signatures by
having 97 or more sections.
Improvements to use modern block list and allow list verbiage.
blacklist -> block list
whitelist -> allow listed
blacklisted -> blocked
whitelisted -> allowed
In the case of certificate verification, use "trust" or "verify" when
something is allowed.
Also changed domainlist -> domain list (or DomainList) to match.
Many of the core scanning functions' names no longer represent their
specific purpose or arguments. This commit aims to make the names more
intuitive. Names are now prefixed with "magic" if they involve
file-typing and file-type parsing. In addition, each function now
includes the type of input being scanned whether its "desc", "fmap", or
"buff". Some of the APIs also now specify "type" to indicate that a type
other than "ANY" may be passed in to select the type rather than use
file type magic for type recognition.
| current name | new name |
| ------------------------- | --------------------------------- |
| magic_scandesc() | cli_magic_scan() |
| cli_magic_scandesc_type() | <delete> |
| cli_magic_scandesc() | cli_magic_scan_desc() |
| cli_base_scandesc() | cli_magic_scan_desc_type() |
| cli_partition_scandesc() | <delete> |
| cli_map_scandesc() | magic_scan_nested_fmap_type() |
| cli_map_scan() | cli_magic_scan_nested_fmap_type() |
| cli_mem_scandesc() | cli_magic_scan_buff() |
| cli_scanbuff() | cli_scan_buff() |
| cli_scandesc() | cli_scan_desc() |
| cli_fmap_scandesc() | cli_scan_fmap() |
| cli_scanfile() | cli_magic_scan_file() |
| cli_scandir() | cli_magic_scan_dir() |
| cli_filetype2() | cli_determine_fmap_type() |
| cli_filetype() | cli_compare_ftm_file() |
| cli_partitiontype() | cli_compare_ftm_partition() |
| cli_scanraw() | scanraw() |
A way is needed to record scanned file names for two purposes:
1. File names (and extensions) must be stored in the json metadata
properties recorded when using the --gen-json clamscan option. Future
work may use this to compare file extensions with detected file types.
2. File names are useful when interpretting tmp directory output when
using the --leave-temps option.
This commit enables file name retention for later use by storing file
names in the fmap header structure, if a file name exists.
To store the names in fmaps, an optional name argument has been added to
any internal scan API's that create fmaps and every call to these APIs
has been modified to pass a file name or NULL if a file name is not
required. The zip and gpt parsers required some modification to record
file names. The NSIS and XAR parsers fail to collect file names at all
and will require future work to support file name extraction.
Also:
- Added recursive extraction to the tmp directory when the
--leave-temps option is enabled. When not enabled, the tmp directory
structure remains flat so as to prevent the likelihood of exceeding
MAX_PATH. The current tmp directory is stored in the scan context.
- Made the cli_scanfile() internal API non-static and added it to
scanners.h so it would be accessible outside of scanners.c in order to
remove code duplication within libmspack.c.
- Added function comments to scanners.h and matcher.h
- Converted a TDB-type macros and LSIG-type macros to enums for improved
type safey.
- Converted more return status variables from `int` to `cl_error_t` for
improved type safety, and corrected ooxml file typing functions so
they use `cli_file_t` exclusively rather than mixing types with
`cl_error_t`.
- Restructured the magic_scandesc() function to use goto's for error
handling and removed the early_ret_from_magicscan() macro and
magic_scandesc_cleanup() function. This makes the code easier to
read and made it easier to add the recursive tmp directory cleanup to
magic_scandesc().
- Corrected zip, egg, rar filename extraction issues.
- Removed use of extra sub-directory layer for zip, egg, and rar file
extraction. For Zip, this also involved changing the extracted
filenames to be randomly generated rather than using the "zip.###"
file name scheme.
XLM is a macro language in Excel that was used before VBA (before
1996). It is still parsed and executed by modern Excel and is gaining
popularity with malware authors.
This patch adds rudimentary support for detecting and extracting
Excel 4.0 (XLM) macros.
The code is based on Didier Steven's plugin_biff for oletools.py.
