TippingPoint Zero Day Initiative

Apple Webkit Button First-Letter Style Rendering Remote Code Execution Vulnerability

ZDI-10-154: August 11th, 2010


CVSS Score

Affected Vendors

Affected Products

TippingPoint™ IPS Customer Protection

TippingPoint IPS customers are protected against this vulnerability by Digital Vaccine protection filter ID 10148. For further product information on the TippingPoint IPS:

Vulnerability Details

This vulnerability allows remote attackers to execute arbitrary code on vulnerable installations of Apple Safari's Webkit. Authentication is not required to exploit this vulnerability. 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 Webkit's support of the 'first-letter' css style. If a particular container has the first-letter style applied to it, the library will create a dual reference of text associated with the style for rendering. Later upon repainting or style recalculation, the application will access the freed memory which can lead to code execution under the context of the application.

Vendor Response

Apple states:

this issue was fixed in Safari 5.0

Disclosure Timeline

    2010-06-01 - Vulnerability reported to vendor
    2010-08-11 - Coordinated public release of advisory


This vulnerability was discovered by:
    wushi of team509