Date: Fri, 15 Jul 2011 10:47:44 +1000 From: Erik de Castro Lopo <erikd@...a-nerd.com> To: Jan Lieskovsky <jlieskov@...hat.com> Cc: oss-security@...ts.openwall.com, "Steven M. Christey" <coley@...us.mitre.org>, Secunia Research <vuln@...unia.com> Subject: Re: CVE Request -- libsndfile -- Integer overflow by processing certain PAF files Please CC me on all mails regarding this bug. I am not on the list where Dan Rosenberg wrote: > On Thu, Jul 14, 2011 at 2:49 AM, Erik de Castro Lopo > <erikd (AT) mega-nerd (DOT) com> wrote: > > Jan Lieskovsky wrote: > > > >> * *an integer overflow, leading to heap-based buffer overflow flaw was > >> found in the way libsndfile, library for reading and writing of sound > >> files, processed certain PARIS Audio Format (PAF) audio files with > >> crafted count of channels in the PAF file header. A remote attacker > >> could provided a specially-crafted PAF audio file, which once opened by > >> a local, unsuspecting user in an application, linked against libsndfile, > >> could lead to that particular application crash (denial of service), > > > > I agree with everything up to here. > > > >> or, potentially arbitrary code execution with the privileges of the > >> user running the application. > > > > but this is rubbish. The heap gets overwritten with zeros which would > > certainly lead to the application segfaulting. However, there is > > no way for arbitrary code to be executed on amy sane OS with proper > > memory protection. > > This is not a sound assumption. Any sort of partially controlled heap > corruption, even if the data that's being written isn't controllable > by an attacker, should be considered potentially exploitable. Modern > heap exploitation is alive and well - it's worth pointing out that a > recent remote vulnerability in Microsoft IIS FTPD that allowed for a > heap overflow of strictly 0xff bytes was shown to be exploitable, > contradicting Microsoft's claims that it could only cause denial of > service. The code which caused the heap overflow was this: memset (ppaf24->samples, 0, ppaf24->samplesperblock * ppaf24->channels) ; where it was the ppaf24->channels value that was not validated (and ppaf24->samplesperblock is always 10). In future versions of libsndfile ppaf24->samplesperblock will be replaced by a compile time constant value. That means that the heap is overwritten in blocks that are a multiple of 10 bytes which makes it significatly more difficult to exploit. > Think about partially overwriting certain elements of heap > metadata, or even heap data, with zeroes. Suppose an application with > heavy function pointer usage was linked against libsndfile, and this > overflow allowed overwriting the least significant bytes of a function > pointer with zeroes and ultimately allowed for controlling execution > flow. For this instance of heap overflow (overwritten in multiples of 10 bytes with the base being 4 byte aligned), its only possible to zero the lowest 2 bytes of a function pointer (assuming a little endian machine) if it happens to lie in exactly the right place. In terms of ease of exploitation, this one has to be in the very difficult basket. > It's better to be safe than sorry. That's why I rushed out a new release. I do take this seriously, but I do not like to see the threat exaggerated beyond reason. Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/
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