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

https://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

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TippingPoint IPS customers have been protected against this
vulnerability by Digital Vaccine protection filter ID 11087. 
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-- 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:
https://support.apple.com/kb/HT4606
https://support.apple.com/kb/HT4607
https://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

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