It was discovered that pango did not check for memory reallocation failures in hbbufferensure() function. This could trigger a NULL pointer dereference in hbbufferaddglyph(), where possibly untrusted input is used as an index used for accessing members of the incorrectly reallocated array, resulting in the use of NULL address as the base array address. This can result in application crash or, possibly, code execution.

It was demonstrated that it's possible to trigger this flaw in Firefox via a specially crafted web page.

Mozilla bug report (currently not public): https://bugzilla.mozilla.org/showbug.cgi?id=606997

Fix in the harfbuzz git: http://cgit.freedesktop.org/harfbuzz/commit/?id=a6a79df5fe2e

Acknowledgements:

Red Hat would like to thank Mozilla Security Team for reporting this issue.

A heap-based buffer overflow, leading to array index error was found in the way the Pango font rendering library rendered glyph box for certain FTBitmap objects, when the FreeType2 Pango back end was used for rendering. If an attacker created a specially-crafted font file and tricked a local, unsuspecting user into loading the font file in an application that uses the Pango font rendering library and FreeType2 Pango back end was used for rendering, it could cause that application to crash or, potentially, execute arbitrary code with the privileges of the user running the application.

References: [1] https://bugs.launchpad.net/ubuntu/+source/pango1.0/+bug/696616

CVE Request: [2] http://www.openwall.com/lists/oss-security/2011/01/18/6

Public PoC: [3] https://bugs.launchpad.net/ubuntu/+source/pango1.0/+bug/696616/comments/1 (malicious font) [4] https://bugs.launchpad.net/ubuntu/+source/pango1.0/+bug/696616/comments/2 (sample text file to trigger the crash)