ZDI-11-104: (Pwn2Own) Webkit CSS Text Element Count Remote Code Execution Vulnerability

http://www.zerodayinitiative.com/advisories/ZDI-11-104

April 14, 2011

-- CVE ID:
CVE-2011-1290

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

-- Affected Vendors:
WebKit

-- Affected Products:
WebKit WebKit

-- TippingPoint(TM) IPS Customer Protection:
TippingPoint IPS customers have been protected against this
vulnerability by Digital Vaccine protection filter ID 11087. 
For further product information on the TippingPoint IPS, visit:

    http://www.tippingpoint.com

-- Vulnerability Details:
This vulnerability allows remote attackers to execute arbitrary code on
vulnerable installations of Webkit. User interaction is required to
exploit this vulnerability in that the target must visit a malicious
page or open a malicious file.

The specific flaw exists within the WebKit library's implementation of a
CSS style. When totaling the length of it's string elements, the library
will store the result into a 32bit integer. This value will be used for
an allocation and then later will be used to initialize the allocated
buffer. Due to the number of elements being totaled being variable, this
will allow an aggressor to provide as many elements as necessary in
order to cause the integer value to wrap causing an under-allocation.
Initialization of this data will then cause a heap-based buffer
overflow. This can lead to code execution under the context of the
application.

-- Vendor Response:
Apple patch on April 14, 2011:
http://support.apple.com/kb/HT4606
http://support.apple.com/kb/HT4607
http://support.apple.com/kb/HT4596

-- Disclosure Timeline:
2011-03-31 - Vulnerability reported to vendor
2011-04-14 - Coordinated public release of advisory

-- Credit:
This vulnerability was discovered by:
    * Anonymous
    * Vincenzo Iozzo, Willem Pinckaers, and Ralf-Philipp Weinmann

-- About the Zero Day Initiative (ZDI):
Established by TippingPoint, The Zero Day Initiative (ZDI) represents 
a best-of-breed model for rewarding security researchers for responsibly
disclosing discovered vulnerabilities.

Researchers interested in getting paid for their security research
through the ZDI can find more information and sign-up at:

    http://www.zerodayinitiative.com

The ZDI is unique in how the acquired vulnerability information is
used. TippingPoint does not re-sell the vulnerability details or any
exploit code. Instead, upon notifying the affected product vendor,
TippingPoint provides its customers with zero day protection through
its intrusion prevention technology. Explicit details regarding the
specifics of the vulnerability are not exposed to any parties until
an official vendor patch is publicly available. Furthermore, with the
altruistic aim of helping to secure a broader user base, TippingPoint
provides this vulnerability information confidentially to security
vendors (including competitors) who have a vulnerability protection or
mitigation product.

Our vulnerability disclosure policy is available online at:

    http://www.zerodayinitiative.com/advisories/disclosure_policy/

Follow the ZDI on Twitter:

    http://twitter.com/thezdi