Date: Wed, 18 Apr 2012 02:32:58 -0400 From: Rich Felker <dalias@...ifal.cx> To: oss-security@...ts.openwall.com Cc: musl@...ts.openwall.com Subject: Stack-based buffer overflow in musl libc 0.8.7 and earlier Name: Stack-based buffer overflow in musl libc 0.8.7 and earlier Software: musl 0.8.7 and earlier Software link: http://www.etalabs.net/musl Vulnerability Type: Buffer overflow Severity: Critical Software Description: musl is an implementation of the C/POSIX standard library for Linux-based systems. musl aims to be lightweight, fast, simple, free, and correct in the sense of standards-conformance and safety, and to meet requirements ranging from embedded systems and initrd images to desktop workstations, mobile devices, and high-load servers. Several build-from-source mini-distributions use musl as their C library. Vulnerability Details: musl's implementation of [v]fprintf swaps in a temporary FILE buffer on the stack when writing to unbuffered streams such as stderr. Under certain conditions where the buffer end pointer has already been set to the address of the internal degenerate buffer prior to the call to [v]fprintf, stdio internals can fail to bound access to the temporary buffer. Large writes will then overflow the temporary buffer and clobber stack contents, including potentially the return address. Any program linked to musl which includes potentially-large data from untrusted sources in its output to stderr or other unbuffered streams is affected. Solution: The vulnerability has been fixed in git, and the fix is to be included in the upcoming 0.8.8 release. A patch which applies cleanly to all recent releases is available on the musl mailing list: http://www.openwall.com/lists/musl/2012/04/17/1 Credits: This vulnerability was discovered and fixed by the author (myself, Rich Felker) while debugging a crash occurring in test code written for musl by Luka Marčetić as part of GSoC 2011.
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