A new zero-day vulnerability in Adobe Reader has been disclosed, once again putting the popular PDF reader in possible peril from attackers.

The newly discovered vulnerability affects "all currently supported shipping versions" of the software, meaning Versions 9.1, 8.1.4, 7.1.1, and earlier of Adobe Reader and Acrobat, and on all operating system platforms for the applications, said Adobe's Product Security Incident Response Team (PSIRT) in its blog this afternoon.

The company is also "currently investigating" the exploit that also was posted with the vulnerability disclosure, blogged Adobe's David Leone.

"Adobe plans to provide updates for all affected versions for all platforms (Windows, Macintosh, and Unix) to resolve this issue. We are working on a development schedule for these updates and will post a time line as soon as possible. We are currently not aware of any reports of exploits in the wild for this issue," blogged Leone.

This is the second major zero-day flaw to be exposed in Adobe Reader this year. In February, Adobe reported a buffer overflow bug in Reader and Acrobat. A researcher later demonstrated that a user merely storing -- and not even opening -- a PDF infected via the flaw could trigger an attack.

With Adobe Reader's security woes increasing during the past few months, some security experts are declaring it time for users to change their PDF reader programs to avoid attacks. F-Secure has led the charge, noting that 47 percent of the targeted attacks it has seen so far this year used Adobe Acrobat Reader PDFs -- a twenty-fold increase compared to last year. "Adobe is targeted primarily because they are the big guy," says Patrik Runald, chief security advisor for F-Secure.

F-Secure now advises users to switch over to an alternative PDF reader from the pdfreaders site for open-source PDF readers. The more diverse the PDF reader pool, the better for user security, Runald says.

Meanwhile, details about the new Reader zero-day are sketchy, other that it being JavaScript-based. "Right now, we don't know too much," Runald says. "There are two different vulnerabilities, one affecting the getAnnots() JavaScript function and the other targeting the spell.customDictionaryOpen() JavaScript function."

Like many third-party plug-in applications, users -- especially consumers -- don't regularly update their Adobe Reader apps. Microsoft recently reported in its Security Incident Report that 90 percent of vulnerabilities in Windows machines are in third-party apps running on them. That has prompted efforts like that of Secunia to rally other software vendors to develop an industry-standard tool that automatically updates all applications on a consumer's PC.

F-Secure says consumers have no reason to be limited to using Acrobat Reader if all they want to do is view PDF files. "Instead of using a tool that is 42 megabytes in size, there are alternatives that are just a few megabytes in size," Runald says.

The main way to protect yourself from Acrobat Reader-borne attacks is to disable JavaScript. That entails unchecking the box "Enable Acrobat JavaScript" under the Preferences tab and clicking "OK," according to Adobe.

The company said in its blog that it has contacted antivirus and security vendors about the vulnerability.

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