[clamav-users] Clam AV large file scan behaviour

Micah Snyder (micasnyd) micasnyd at cisco.com
Mon Mar 11 17:36:06 EDT 2019


Hi Gareth,

Sorry about the delay in response.
No this is not expected behavior.  Inconsistencies in the actual max file size is a known issue, particularly on Windows and 32bit systems.  The issues noted in this bug report in particular are probably the leading causes: 
https://bugzilla.clamav.net/show_bug.cgi?id=12251.

I suspect that 2GB may be the max file size that can be consistently scanned by ClamAV at this time. 

As this is a bug, there is no other mechanism to force an error message to occur when it fails to scan the entire file. I hope we'll be able to find time to resolve the large file issue soon, and I apologize for the inconvenience.

Micah


Micah Snyder
ClamAV Development
Talos
Cisco Systems, Inc.
 




On 2/25/19, 9:36 AM, "clamav-users on behalf of Gareth Williams via clamav-users" <clamav-users-bounces at lists.clamav.net on behalf of clamav-users at lists.clamav.net> wrote:

    Hello,
    
    We have been using ClamAV for several months, and are noticing some strange behaviour when scanning files (and archives) above a certain size.
    
    The documentation states:
    --max-filesize=#n can be anything up to 4GB
    --max-scansize=#n can be anything up to 4GB
    
    We are however experiencing different behaviour:
    
    Scanning a file of ~3GB in size results in no scan taking place, but reporting the file is OK anyway.
    
    COMMAND:
    clamscan --max-scansize=4000M --max-filesize=4000M -rav --block-max=yes --max-recursion=5 --max-dir-recursion=4 Users.xml
    
    OUTPUT:
    Scanning Users.xml
    Users.xml: OK
    
    ----------- SCAN SUMMARY -----------
    Known viruses: 6813534
    Engine version: 0.101.1
    Scanned directories: 0
    Scanned files: 1
    Infected files: 0
    Data scanned: 0.00 MB <=================
    Data read: 2955.02 MB (ratio 0.00:1)
    Time: 12.935 sec (0 m 12 s)
    
    As this file is less than 4GB, we would have expected this to have been scanned properly.
    
    
    We have also noted erratic behaviour when scanning archive files. For example:
    
    COMMAND:
    clamscan --max-scansize=4000M --max-filesize=4000M -rav --block-max=yes --max-recursion=5 --max-dir-recursion=4 stackoverflow.com-Users.7z
    
    OUTPUT:
    Scanning stackoverflow.com-Users.7z
    Scanning stackoverflow.com-Users.7z!7Z:Users.xml
    stackoverflow.com-Users.7z: OK
    
    ----------- SCAN SUMMARY -----------
    Known viruses: 6813534
    Engine version: 0.101.1
    Scanned directories: 0
    Scanned files: 1
    Infected files: 0
    Data scanned: 413.86 MB
    Data read: 410.01 MB (ratio 1.01:1)
    Time: 28.029 sec (0 m 28 s)
    
    This archive contains the same file as in the first example, and it does not appear to extract the file from the archive. It simply scan the archive itself. We have observed other cases where archives are extracted and scanned fully by clamscan.
    
    
    Questions:
    - Is this expected behaviour for clamscan?
    
    - Is there another, lower, limit on file sizes which can actually be scanned in practice?
    
    - Is there a way to force clamscan to error if a file has not actually been scanned?
    
    
    Regards,
    
    Gareth
    
    
    
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