Date: Mon, 7 Aug 2006 12:45:03 -0500
From: Bryan <bryan.madhatter@...il.com>
To: "Bipin Gautam" <gautam.bipin@...il.com>
Cc: full-disclosure@...ts.grok.org.uk, bugtraq@...urityfocus.com
Subject: Re: when will AV vendors fix this???

So it's the AV vendor's responsibility to fix the permissions within the
OS?  Personally,
I'd be annoyed if my AV started randomly changing file permissions.  On top
of the fact,
you would need access to the machine to reset permissions on the
file/directory/etc.
before the AV scan took place.  So unless you already have access to the
machine or
can convince the user to execute cacls this doesn't seem like much of a
problem.  In
the first case, there are worse problems than how the AV runs and in the
second you
can't really cure stupid users since if they execute the command it's
performing by design.

Bryan

On 8/5/06, Bipin Gautam <gautam.bipin@...il.com> wrote:
>
> hello list,
>
> This is actually a DESIGN BUG OF MOST(ALL?) Antivirus & trojan
> scanners. ( ROOTKIT SCANNERS already DO THIS ) This issue is a MORE
> THAN 1 YEAR OLD stuff but i see no fix till now!!!!
>
> lately i've ONLY tested it on the following AV & few other spyware
> scanner & saw its still NOT fixed!
>
> Kaspersky Anti-Virus 6.x (latest)
> BitDefender 9 Professional Plus (latest)
> NOD32 (latest)
>
> OS tested: WINxp sp2
>
> to keep things simple, let me give you a situation;
>
> if there is a directory/file a EVIL_USER is willing to hide from
> antivirus scanner all he has to do is fire up a command prompt & run
> the command;
>
> cacls.exe TORJANED_FILE_OR_DIRECTORY_NAME /T /C /P EVIL_USER:R
>
>
> next time EVEN when the administrator starts the antivirus "system
> scan" the TORJANED_FILE_OR_DIRECTORY_NAME   will be effectively
> bypassed as the ownership of the directory is just of the user account
> named; EVIL_USER and the antivirus "manual scan" is running just with
> the privilage of ADMINISTRATOR
>
>
> by this way a malicious executable can remain hidden in the system
> BYPASSING THE SCAN even when the AV scanner is run by administrator!!!
>
> BUT there isn't a compulsion that there should be a user with a
> malicious intension to get this condition & bypass the scan.
>
> there is another DUMB equivalent of the above cacls.exe command;
> Right click a folder, Properties > Sharing Tab >> Check on the tick
> mark of >> Make this Folder Private
>
> by doing so a user might me thinking he is making a folder
> not_accessable_to_any_other_system_user BUT by doing so... the
> directory gets effectively sciped by a AV scannner vulnerable to this
> trick.
>
>
> SOLUTION:
> AV already running with administrative privilage if the system
> administrator is starting manual scan, so what does AV should do is
> excelate its (manual scan) OF THE ANTIVIRUS SCANNER ENGINE/DRIVER (not
> the GUI) privilage to SYSTEM before starting the scan which will
> effectively bypass file permission & be able to scan the locked file
> with any file permission in Windows!
>
> And one more thing, if during AV scan if a file can't be opened due to
> some processes LOCKING the file.... Instead of going through the
> regular file open  process AV should instead directly read the SECTORS
> of the hdd holding the locked file and examine if there is sething
> malicious (which still some AV don't do & instead just report the
> file(s) as locked!)
>
> am i clear??? Discussions, welcome!
>
>
> ---
>
> Bipin Gautam
> http://bipin.tk
>
> Zeroth law of security: The possibility of poking a system from lower
> privilege is zero unless & until there is possibility of direct,
> indirect or consequential communication between the two...
>

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