Adobe on Thursday warned that a critical security vulnerability exists in its Acrobat and Reader software.

"This vulnerability would cause the application to crash and could potentially allow an attacker to take control of the affected system," Adobe says in its security advisory. "There are reports that this issue is being exploited."

Symantec security researcher Patrick Fitzgerald explains that the vulnerability is caused by a PDF parsing error. "Once the malicious document is opened it will trigger the vulnerability," he said in a blog post. "The JavaScript payload then sprays the heap with the malicious shellcode in an attempt to increase the chances of a successful exploit. If the exploit is successful, a malicious binary will be dropped and executed on the victim's system."

Fitzgerald says that the malicious payload is a backdoor Trojan that comes from an open source toolkit known as Ghost that originated in China. Once installed on a computer, it allows the attacker to view the victim's desktop, record keystrokes, and access the machine remotely.

The vulnerability affects Adobe Reader 9 and earlier versions, and Adobe Acrobat Standard, Pro, Pro Extended 9, and earlier versions.

Adobe plans to release updates for Acrobat Reader 9 and Acrobat 9 by March 11, with updates for earlier versions of the software to follow.

In the meantime, Steven Adair, a security researcher with Shadowserver Foundation, advises that users disable JavaScript on their computers if they use either Adobe Reader or Adobe Acrobat.

"[W]e found that disabling JavaScript would definitely prevent the malware from being installed on the system," he explained in an online post. "However, it would still result in the crash of the application. We would HIGHLY recommend that you DISABLE JAVASCRIPT in your Adobe Acrobat [Reader] products. You have the choice of small loss in functionality and a crash versus your systems being compromised and all your data being stolen. It should be an easy choice."

In addition, US-CERT recommends preventing PDF documents from being opened automatically in Internet Explorer, disabling the display of PDF documents in any Web browser, and exercising caution when one receives PDF files from an unknown source.

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