ZDI-11-249: (Pwn2Own) Microsoft Internet Explorer Protected Mode Bypass Vulnerability

http://www.zerodayinitiative.com/advisories/ZDI-11-249

August 9, 2011

-- CVSS:
6.4, (AV:N/AC:L/Au:N/C:P/I:P/A:N)

-- Affected Vendors:
Microsoft

-- Affected Products:
Microsoft Internet Explorer

-- TippingPoint(TM) IPS Customer Protection:
TippingPoint IPS customers have been protected against this
vulnerability by Digital Vaccine protection filter ID 11294. 
For further product information on the TippingPoint IPS, visit:

    http://www.tippingpoint.com

-- Vulnerability Details:
This vulnerability allows remote attackers to escape Protected Mode on
vulnerable installations of Internet Explorer.

Internet Explorer Protected Mode consists of a Medium Integrity and a
Low Integrity process. The Low Integrity process is only allowed to
write to special Low Integrity locations. File written there are marked
as Low Integrity files. When a new Internet Explorer process is launched
it checks the Integrity of the file it is launched against. If the file
is a Low Integrity file it will run the process in Low Integrity Mode.
It is however possible to give the file an even lower permission:
Untrusted, since this does not match the check for 'Low Integrity' the
Internet Explorer will run in Medium Integrity instead of Low Integrity.
This can be abused in an exploit to bypass the Protected Mode design and
thus allow an attacker to escalate their privileges.

-- Vendor Response:
Microsoft has issued an update to correct this vulnerability. More
details can be found at:
http://www.microsoft.com/technet/security/bulletin/MS11-057.mspx

-- Disclosure Timeline:
2011-03-09 - Vulnerability reported to vendor
2011-08-09 - Coordinated public release of advisory

-- Credit:
This vulnerability was discovered by:
    * Stephen Fewer of Harmony Security (www.harmonysecurity.com)

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