funsec mailing list archives
RE: Overloading AV software, was Question about Viruses
From: "Richard M. Smith" <rms () bsf-llc com>
Date: Fri, 7 Jul 2006 14:13:24 -0400
Regardless of how difficult it might be to put a virus signature into an image file, one should be able to create a Web page which downloads hundreds of small files which cause an false alarms to be trigger by an AV software package, right? Besides my little VBScript file, one could use real virus files that are downloaded via an <img src=> tag. BTW, my VBScript file is triggering some sort of Bloodhound signature. I've seen similar Bloodhound warnings for WMF files. Here's my VBScript code which is very generic: rem rem Library of VBScript helper functions which can be called from JavaScript rem Function VBSByteArray2String(BA) Dim j, n n = UBound(BA) + 1 Execute "Dim a(" & CStr(n) & ")" ' Isn't there any easier way to create a dynamic array in VBSCript? BA = Midb(BA, 1, n) ' Without this useless midb call, this function runs very slow For j = 1 to n a(j - 1) = ChrW(Ascb(Midb(BA, j, 1))) 'ChrW is very important Next VBSByteArray2String = Join(a, "") End Function Function VBSEval(expr) VBSEval = eval(expr) End Function Function VBSArrayLen(a) VBSArrayLen = UBound(a) + 1 End Function Function VBSTypeName(a) VBSTypeName = TypeName(a) End Function Function VBSVarType(a) VBSVarType = VarType(a) End Function Function VBSFormatDateTime(d, format) VBSFormatDateTime = FormatDateTime(d, format) End Function Function VBSVerno Dim s s = "" s = s & ScriptEngineMajorVersion & "." s = s & ScriptEngineMinorVersion & "." s = s & ScriptEngineBuildVersion VBSVerno = s End Function Function VBSGetLocale VBSGetLocale = GetLocale() End Function Function VBSTimeSplit(time) VBStimeSplit = Array(Year(time), Month(time), Day(time), Hour(time), Minute(time), Second(time)) End Function Richard -----Original Message----- From: Drsolly [mailto:drsollyp () drsolly com] Sent: Friday, July 07, 2006 2:00 PM To: Richard M. Smith Cc: 'FunSec LList' Subject: RE: [funsec] Overloading AV software, was Question about Viruses On Fri, 7 Jul 2006, Richard M. Smith wrote:
But for the most part massimo is right, it's a dumb strategyHmm, what if the bad guys overloaded a user with virus warning messages as
a
stratergy to get people to turn off their AV software. For example, could
a
Web page download a few hundred image files with known virus signatures tacked on the end of each file in order to make AV software go nuts?
Could
the same trick be used in an HTML email message?
You have a fundamental (and very common) misunderstanding about "virus signatures". I can only talk authoritatively about my AV software design, but I think most AV software today works in a similar way. So. The problem is, you think there's something called a "virus signature". There is, indeed, an "Alan Solomon" signature, I write it on cheques and suchlike, and it's pretty much the same each time I write it, and you can reognise that it's my signature. But there is no similar "virus signature". What there is, is a sequence of bytes chosen from the body of the virus, that the AV uses to determine whether the virus is present or not. 1) Different AV products will choose different sequences as the thing they're looking for. 2) Certainly the AV I wrote (and it still works this way today), and (I think) most other AV products, only look for that byte sequence, in the place(s) that it would have to be if the file is infected. So, if you append that byte-sequence to the end of the file, the AV will, correctly, say that the file is not infected. So, your idea won't work.
I already have an HTML application that is triggering false positives in Symantec because Symantec thinks a bit of VBScript code I wrote is a malicious code.
That's a false alarm. Send Symantec the code you wrote, explain that it's generating false alarms, and wait for them to fix their product. _______________________________________________ Fun and Misc security discussion for OT posts. https://linuxbox.org/cgi-bin/mailman/listinfo/funsec Note: funsec is a public and open mailing list.
Current thread:
- Question about Viruses Dude VanWinkle (Jul 07)
- Re: Question about Viruses <...> (Jul 07)
- RE: Question about Viruses Larry Seltzer (Jul 07)
- RE: Overloading AV software, was Question about Viruses Richard M. Smith (Jul 07)
- RE: Overloading AV software, was Question about Viruses Drsolly (Jul 07)
- RE: Overloading AV software, was Question about Viruses Richard M. Smith (Jul 07)
- Re: Overloading AV software, was Question about Viruses Dude VanWinkle (Jul 07)
- Re: Overloading AV software, was Question about Viruses Drsolly (Jul 07)
- Re: Overloading AV software, was Question about Viruses Dude VanWinkle (Jul 07)
- Re: Question about Viruses Peter Kosinar (Jul 07)
- Re: Re: Question about Viruses Drsolly (Jul 07)
- Re: Re: Question about Viruses Peter Kosinar (Jul 07)
- Re: Re: Question about Viruses Valdis . Kletnieks (Jul 07)
- Re: Re: Question about Viruses Peter Kosinar (Jul 07)
- Re: Re: Question about Viruses Drsolly (Jul 07)
- RE: Question about Viruses Larry Seltzer (Jul 07)
- Re: Question about Viruses <...> (Jul 07)
- Re: Re: Question about Viruses Dude VanWinkle (Jul 08)