'Better than Adobe' Foxit PDF plugin hit by worse-than-Adobe 0-day

A new security bug in the popular Foxit PDF reader plugin for web browsers allows miscreants to compromise computers and install malware. There's no patch for this zero-day vulnerability.

Italian security researcher Andrea Micalizzi discovered that the latest version of the software crashes if users are tricked into clicking on an overly long web link. The plugin is kicked into action by the browser to handle the file and promptly bombs.

But the bug is not triggered by a booby-trapped document, which is the usual way of infecting systems running insecure PDF readers. Instead, clicking on a link to any PDF that deliberately includes a very long query string after the filename causes a buffer overflow in the Foxit plugin.

The offending code, highlighted by Micalizzi, is a simple loop that copies the entire URL into a fixed-sized buffer while scanning for '%' escape codes. By smashing through the end of this buffer, the attacker can arbitrarily overwrite the program's memory and its stack to gain control of the processor.

Versions 5.4.4.1128 and older are affected. The plugin is available for a number of operating systems, including Linux and Symbian, but the bug is at least confirmed in the Microsoft Windows build.

Other security researchers have confirmed the flaw. A proof-of-concept exploit for the hole was not made available in Micalizzi's disclosure.

"The crash, which is a side-effect of a stack overflow, pretty much lets you write to a memory location of your choice," said Paul Ducklin, Sophos's head of technology for Asia Pacific.

Foxit can be installed for Mozilla Firefox, Google Chrome, Opera and Apple Safari. Danish vulnerability management firm Secunia rates the flaw as highly critical. The makers of Foxit - which is billed as "better than Adobe" - have yet to comment on the issue.

Many fans of Foxit have adopted the software as a way of avoiding the not infrequent security problems with Adobe PDF Reader. The appearance of the Firefox plugin vulnerability is further evidence that no software application is immune to security problems. ®