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Bug-hunt turns up vuln in LibreSSL
Code review: it works
Updated Code reviewers looking over a mail daemon have turned up a couple of reasonably serious bugs in the Libre SSL code base – and along the way provided a handy illustration of the deep interdependencies between software.
What they've found is that there's a companion memory leak (CVE-2015-5333) and buffer overflow (CVE-2015-5334) in the SSL replacement candidate.
The researchers from Qualys (their notice published here) said they were trying to see if a remote code execution attack is feasible against vulnerabilities they've turned up in OpenSMTPD (which earlier this month hit version 5.7.3).
“Because we could not find one in OpenSMTPD itself, we started to review the malloc()s and free()s of its libraries, and eventually found a memory leak in LibreSSL's OBJ_obj2txt() function; we then realized that this function also contains a buffer overflow (an off-by-one, usually stack-based).”
The memory leak provides a path for an attacker to cause a denial-of-service attack, and also permits triggering of the buffer overflow.
The buffer overflow exists because of a change to OBJ_obj2txt() which can write a null terminator out of bounds, and the resulting crash might provide a path for remote code execution.
As the code reviewers note, however, because it's stack-based it's “probably not exploitable on OpenBSD x86, where it appears to always smash the stack canary”.
The LibreSSL team has released fixes for OpenBSD. ®