Date: Fri, 9 Jan 2009 13:36:24 -0500 (EST) From: Josh Bressers <bressers@...hat.com> To: oss-security <oss-security@...ts.openwall.com> Subject: libpng non issue I figured I'd put this out in the open before it gets picked up and causes confusion. The libpng main page (http://libpng.sourceforge.net/index.html) currently contains this: UPDATE 18 December 2008: The latest released versions are libpng-1.0.42 and libpng-1.2.34. They fix a vulnerability to a possible double-free in png_check_keyword() while writing various chunk types. This isn't a double free, nor would I consider it a security bug. Our libpng maintainer Tom Lane helped out with this analysis. As best as I can tell, this is the bug in question: http://sourceforge.net/mailarchive/forum.php?thread_name=4B6F0239C13D0245820603C036D180BC79FBAA%40CABOTUKEXCH01.cabot.local&forum_name=png-mng-implement which results in writing a NULL byte to an arbitrary location in memory. Here is what Tom Lane said about this: Some poking around shows that png_check_keyword is called in subroutines that *write* PNG chunks, not ones that read them. So the problem could only manifest in programs that were creating new PNG files and trying to put illegal-per-spec content in them. Also, in typical usage the keywords being checked would be constant strings in the app, thus even less likely to trigger the overlength error. (It seems likely that this code has actually never been executed anywhere, explaining why the bug went undetected.) So unless someone sees a flaw in this analysis, Red Hat has no plans to consider this a security flaw. Thanks. -- JB
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