Virus False Positive

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Revision as of 15:16, 21 April 2017 by JohnMertz (talk | contribs) (Decoding a ClamAV Signature)

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CanIt uses Clam Antivirus as the primary method for detecting viruses within attachments. ClamAV works by looking for known Virus Signatures, a certain segment of code that can be used to identify the specific malicious behaviour. This method will in, rare instances, provide false-positives if a signature was wrongly or poorly identified.

Decoding a ClamAV Signature

Before taking any steps to remove or ignore a signature you should first determine whether it is, in fact, overly aggressive. From the command line of a CanIt appliance or any other Linux machine with ClamAV installed you can run:

 sigtool --find-sigs=Sanesecurity.Virus.Code.### | sigtool --decode

For example:

 # sigtool --find-sigs=Sanesecurity.Phishing.Fake.26397 | sigtool --decode
 VIRUS NAME: Sanesecurity.Phishing.Fake.26397
 TARGET TYPE: HTML
 OFFSET: *
 DECODED SIGNATURE:
 unusual activity on your paypai

Request Removal

The source that ClamAV uses to aggregate these signatures is SaneSecurity. You can report the false-positive to them at this address:

 http://sanesecurity.com/support/false-positives/

Manual Removal (CanIt-Pro and Domain-Pro only)

If you'd like ClamAV to ignore specific virus signatures, this needs to be defined an all machines as follows:

Append to local 'ignore' file, where 'Sanesecurity.Virus.Code.###' is the name of the signature as defined in the "detail=" header of the false-positive:

 echo 'Sanesecurity.Virus.Code.###' >> /var/lib/clamav/local.ign2

Restore ownership of the 'ignore' file to the clamav user:

 chown clamav:clamav /var/lib/clamav/local.ign2

Restart ClamAV:

 /etc/init.d/clamav-daemon force-reload