Critical vulnerability in Adobe Reader
Posted on 04 November 2008.
Core Security Technologies issued an advisory disclosing a vulnerability that could affect millions of individuals and businesses using Adobe’s Reader PDF file viewing software. Engineers from CoreLabs determined that Adobe Reader could be exploited to gain access to vulnerable systems via the use of a specially crafted PDF file with malicious JavaScript content. Upon making the discovery, CoreLabs immediately alerted Adobe to the vulnerability and the two companies have since coordinated efforts to ensure that a patch could be created and made available to protect users of the program.

Successful exploitation of the vulnerability requires that users open a maliciously crafted PDF file thereby allowing attackers to gain access to vulnerable systems and assume the privileges of a user running Acrobat Reader. Adobe Reader version 9, which was released in June 2008, is not vulnerable to the reported problem.

Adobe has issued a security update that addresses the vulnerable version 8.1.2 of Reader. Alternatively, users of affected versions of the program can also work around the problem and reduce their exposure by disabling JavaScript functionality in the software’s Edit|Preferences menu.

Vulnerability details

While investigating the feasibility of exploiting a vulnerability previously disclosed in Foxit Reader (CVE-2008-1104), a CoreLabs researcher found that Adobe Reader was affected by the same bug.

After an initial examination of the involved implementation bug, it was believed that although the problem was present, it was apparently not exploitable in Adobe Reader due to the use of two structured exception handlers in the program. The primary difference between the Adobe and Foxit applications is the manner in which they perform security checks, and at first glance, it seemed as if the bug was not exploitable in Reader, since there was no way to control the program’s first exception handler.

However, upon further examination of the code, CoreLabs found that another overflow occurs before the call to the involved code is made in relation to the previously known vulnerability. This new problem was identified in the way vulnerable versions of Adobe Reader implement the JavaScript util.printf() function. The function first converts the argument it receives to a String, using only the first 16 digits of the argument and padding the rest with a fixed value of “0” (0x30). By passing an overly long and properly formatted command to the function, it is possible to overwrite the program’s memory and control its execution flow.

A specifically crafted PDF file that embeds JavaScript code to manipulate the program’s memory allocation pattern and trigger the vulnerability can allow an attack to execute arbitrary code with the privileges of a user running the Adobe Reader application.

The vulnerability was discovered by Damián Frizza, a CoreLabs researcher and software engineer with the CORE IMPACT Exploit Writers Team. The previously disclosed vulnerability (CVE-2008-1104) mentioned in this report was discovered in Foxit Reader by Dyon Balding from Secunia Research and disclosed on May 20th, 2008.





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