full-disclosure - when will AV vendors fix this???

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Date: Sat, 5 Aug 2006 13:05:56 +0545
From: "Bipin Gautam" <gautam.bipin@...il.com>
To: full-disclosure@...ts.grok.org.uk, bugtraq@...urityfocus.com
Cc: 
Subject: when will AV vendors fix this???

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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