Firefox 39 Out With Patches for Four Critical Vulnerabilities

Mozilla has rolled out a new version of its Firefox browser, an update that includes patches for four critical security vulnerabilities and several less-severe bugs.

Mozilla has rolled out a new version of its Firefox browser, an update that includes patches for four critical security vulnerabilities and several less-severe bugs.

IN all, Firefox 39 patches 13 vulnerabilities, including two high-risk bugs and six moderate-level ones. The most dangerous vulnerabilities, however, include a pair of use-after-free bugs in one part of the browser and another in a separate component, as well as a number of memory corruption flaws.

“Security researcher Looben Yan used the Address Sanitizer tool to discover two related use-after-free vulnerabilities that occur when using XMLHttpRequest in concert with either shared or dedicated workers. These errors occur when the XMLHttpRequest object is attached to a worker but that object is incorrectly deleted while still in use. This results in exploitable crashes,” the Mozilla advisory says.

The other use-after-free flaw is in the Content Policy component of Firefox.

“Security researcher Herre reported a use-after-free vulnerability when a Content Policy modifies the Document Object Model to remove a DOM object, which is then used afterwards due to an error in microtask implementation. This leads to an exploitable crash,” the advisory says.

In addition, the critical bugs also include the memory corruption flaws, and a potpourri of bugs a researcher discovered through code inspection.

“Security researcher Ronald Crane reported seven vulnerabilities affecting released code that he found through code inspection. These included three uses of uninitialized memory, one poor validation leading to an exploitable crash, one read of unowned memory in zip files, and two buffer overflows. These do not all have clear mechanisms to be exploited through web content but are vulnerable if a mechanism can be found to trigger them,” the advisory says.

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