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More issues with 0.99.3 beta 1
I have two files which are being wrongly reported as infected by 0.99.3 beta 1. ClamAV 0.99.2 doesn't detect any issues with the files.

The first is a single email file (extension .emlx) with md5 checksum of 245ec37768c235da265014add38bdf4d and a file size of 2777 bytes. It's being detected as Win.Trojan.Agent-6319774-0 which has the following signature in daily.cvd

[daily.hsb] 6f8f57715090da2632453988d9a1501b:1:Win.Trojan.Agent-6319774-0:73

Three things strike me as odd about this:
1) The length of that hash surely matches md5 rather than sha1/sha256 and therefore ought to be in an hdb file rather than hsb?
2) It specifies a length of 1 byte, but also has :73 at the end which means "file size unknown".
3) The hash doesn't even match the hash of the email file in question. FWIW 163 other different email files are also triggering the same infection on 0.99.3 but not 0.99.2

Wouldn't either of the first two be enough for the sig to be marked as corrupt?

Lastly, why are ClamAV 0.99.2 and 0.99.3 treating that signature differently?


The other file is a PDF being wrongly detected as Win.Trojan.Agent-5520346-0. It appears to have the same issue with the signature definition inside daily.hsb, and also the file hash (c6721e7c77846b5a1d0efe3a708d8dc7) doesn't match the signature hash but is still being detected by 0.99.3 That hash can be found on VirusTotal with zero other detections.

[daily.hsb] 8fa14cdd754f91cc6554c9e71929cce7:1:Win.Trojan.Agent-5520346-0:73

While I could just add those two signatures to a local exclude file, I suspect there may be a bigger issue at play with 0.99.3

Hope this is helpful.

Mark

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Re: More issues with 0.99.3 beta 1 [ In reply to ]
Mark,

Thanks, we are also observing these same FP's in our testing. They are on
the roadmap for 0.99.3.

Steve

On Tue, Aug 15, 2017 at 6:34 AM, Mark Allan <markjallan@gmail.com> wrote:

> I have two files which are being wrongly reported as infected by 0.99.3
> beta 1. ClamAV 0.99.2 doesn't detect any issues with the files.
>
> The first is a single email file (extension .emlx) with md5 checksum of
> 245ec37768c235da265014add38bdf4d and a file size of 2777 bytes. It's
> being detected as Win.Trojan.Agent-6319774-0 which has the following
> signature in daily.cvd
>
> [daily.hsb] 6f8f57715090da2632453988d9a1501b:1:Win.Trojan.Agent-6319774-
> 0:73
>
> Three things strike me as odd about this:
> 1) The length of that hash surely matches md5 rather than sha1/sha256 and
> therefore ought to be in an hdb file rather than hsb?
> 2) It specifies a length of 1 byte, but also has :73 at the end which
> means "file size unknown".
> 3) The hash doesn't even match the hash of the email file in question.
> FWIW 163 other different email files are also triggering the same infection
> on 0.99.3 but not 0.99.2
>
> Wouldn't either of the first two be enough for the sig to be marked as
> corrupt?
>
> Lastly, why are ClamAV 0.99.2 and 0.99.3 treating that signature
> differently?
>
>
> The other file is a PDF being wrongly detected as
> Win.Trojan.Agent-5520346-0. It appears to have the same issue with the
> signature definition inside daily.hsb, and also the file hash (
> c6721e7c77846b5a1d0efe3a708d8dc7) doesn't match the signature hash but is
> still being detected by 0.99.3 That hash can be found on VirusTotal with
> zero other detections.
>
> [daily.hsb] 8fa14cdd754f91cc6554c9e71929cce7:1:Win.Trojan.Agent-5520346-
> 0:73
>
> While I could just add those two signatures to a local exclude file, I
> suspect there may be a bigger issue at play with 0.99.3
>
> Hope this is helpful.
>
> Mark
>
>
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Re: More issues with 0.99.3 beta 1 [ In reply to ]
Mark,

> On Aug 15, 2017, at 12:34 PM, Mark Allan <markjallan@gmail.com <mailto:markjallan@gmail.com>> wrote:
>
> 2) It specifies a length of 1 byte, but also has :73 at the end which means "file size unknown".


This is not quite correct, the 1 here should be interpreted as a file size of 1 byte. The trailing :73 is a engine version restriction based on engine functional level, restrictions can have a minimum and maximum version and for HSB sigs are optional trailing fields in the form :F-Min:F-Max. The 73 here refers to an internal test engine release that included this functionality for wildcard size that first appeared in ClamAV 0.98 (which has functional level 74).


Tom
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Re: More issues with 0.99.3 beta 1 [ In reply to ]
Hy,
I know that ClamAV haven't yet developed product for android. But I have
one question for android. Is there any work done on .NET trojans (Android
applications). Because android also supports .NET applications. And the
.NET trojans has been detected even on the android.

I am working on android malware analysis. And I couldn't find any thing on
it.
Can you please help me ...
Thanks

On 16 August 2017 at 13:28, Tom Judge <tjudge@sourcefire.com> wrote:

> Mark,
>
> > On Aug 15, 2017, at 12:34 PM, Mark Allan <markjallan@gmail.com <mailto:
> markjallan@gmail.com>> wrote:
> >
> > 2) It specifies a length of 1 byte, but also has :73 at the end which
> means "file size unknown".
>
>
> This is not quite correct, the 1 here should be interpreted as a file size
> of 1 byte. The trailing :73 is a engine version restriction based on
> engine functional level, restrictions can have a minimum and maximum
> version and for HSB sigs are optional trailing fields in the form
> :F-Min:F-Max. The 73 here refers to an internal test engine release that
> included this functionality for wildcard size that first appeared in ClamAV
> 0.98 (which has functional level 74).
>
>
> Tom
> _______________________________________________
> http://lurker.clamav.net/list/clamav-devel.html
> Please submit your patches to our Bugzilla: http://bugs.clamav.net
>
> http://www.clamav.net/contact.html#ml
>



--
*Abdul Rahman Khan*

*NAMAL College Mianwali*
*Contact# 03044205651*
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