Date: Sun, 18 Jan 2009 19:55:22 +0100 From: Nico Golde <oss-security+ml@...lde.de> To: oss-security@...ts.openwall.com Subject: Re: libpng non issue Hi, * Josh Bressers <bressers@...hat.com> [2009-01-10 15:41]: > 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 Looking at the diff between 1.2.33 and 1.2.34 I also see no fix for a double-free vulnerability. The only security relevant change I can see is indeed the above issue. > 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. As this function symbol is exported via the shared library what about programs using this function? Cheers Nico -- Nico Golde - http://www.ngolde.de - nion@...ber.ccc.de - GPG: 0x73647CFF For security reasons, all text in this mail is double-rot13 encrypted. Content of type "application/pgp-signature" skipped
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