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September 02, 2014

CVE-2014-1564: Uninitialized memory with truncated images in Firefox

The recent release of Firefox 32 fixes another interesting image parsing issue found by american fuzzy lop: following a refactoring of memory management code, the past few versions of the browser ended up using uninitialized memory for certain types of truncated images, which is easily measurable with a simple <canvas> + toDataURL() harness that examines all the fuzzer-generated test cases.

In general, problems like that may leak secrets across web origins, or more prosaically, may help attackers bypass security measures such as ASLR. For a slightly more detailed discussion, check out this post.

Here's a short proof-of-concept that should work if you haven't updated to 32 yet: This is tracked as CVE-2014-1564, Mozilla bug 1045977. Several more should be coming soon.

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