Date: Mon, 20 Jun 2011 09:35:52 +0100 From: Daniel Godás <dgodas@...il.com> To: oss-security@...ts.openwall.com Subject: Re: CVE request: crypt_blowfish 8-bit character mishandling This is the most sensible email I've seen on this list in ages. Keep up the good work! 2011/6/20 Solar Designer <solar@...nwall.com> > Hi, > > Earlier today, while working on a test suite for John the Ripper, magnum > discovered and reported what turned out to be a bug in John the Ripper > and crypt_blowfish: > > http://www.openwall.com/lists/john-dev/2011/06/19/2 > > The bug is inadvertent sign extension, and the fix is trivial: > > http://www.openwall.com/lists/john-dev/2011/06/19/3 > > This bug dates back to 1998 (or maybe even 1997). > > Unfortunately, the bug is not only in JtR, but also in crypt_blowfish, > and thus in plenty of other systems and programs that have integrated > crypt_blowfish. Obviously, I am quite embarrassed; I should have > included 8-bit test vectors or subjected crypt_blowfish to a fuzzer (vs. > OpenBSD's implementation), or/and used different coding conventions (use > "unsigned char" almost everywhere, although this has its problems too - > such as compiler warnings on library calls that expect simple "char *"). > > Since the code successfully worked in JtR, I thought that it was > essentially already fuzz-tested. But apparently passwords with 8-bit > characters were uncommon enough that no one noticed the bug for years. > > I am going to provide an official fix for crypt_blowfish (likely the > one-liner plus added tests). I thought I'd bring the issue up on > oss-security sooner rather than later. > > Here's my preliminary analysis of the impact: > > http://www.openwall.com/lists/john-dev/2011/06/20/3 > http://www.openwall.com/lists/john-dev/2011/06/20/5 > > To summarize: > > The majority of hashes (but not all of them) for passwords containing > characters with the 8th bit set are incompatible with OpenBSD's (really > nasty, but no security impact here). > > What's worse, approximately 3 in 16 passwords containing a single > character with the 8th bit set have 1 to 3 characters immediately > preceding the 8-bit character ignored. With more than one character > with the 8th bit set, things may be even worse. > > Thus, those passwords may be much easier to crack than expected. > > As to what's affected besides crypt_blowfish itself, I expect it to be > PHP (the code in php-5.3.7RC1 looks affected), Linux distros that use > crypt_blowfish (Owl, ALT Linux, SUSE), and some others (I'll try to > identify them and notify the maintainers). > > Sorry about that! > > Since this is the second bug with char signedness in crypt_blowfish, it > looks like I have a lesson to learn here. The last time, the bug was > with salt generation for hash types other than bcrypt (that code was > little used and little tested). Besides fixing the bug, I responded by > running extensive tests and making sure the distribution of salts was > uniform. Of course, it was better to run those tests before releasing > the code to the public. Now we have an issue with the passwords > themselves. Obviously, I will be adding more tests, even though it > would be better done before releasing the code. > > No, I don't expect even more sign extension bugs in crypt_blowfish. > There's not that much code, and we've pretty much tested it by now. > > However, I might reconsider my C programming conventions for new code as > it relates to use of integer types. I think I'd rather workaround > meaningless compiler warnings on strlen() and the like (even though > those extra casts look dirty) than miss real bugs elsewhere. > > Perl's Crypt::Eksblowfish turns out to have sufficiently reworked code > that it's unaffected: > > http://www.openwall.com/lists/john-dev/2011/06/20/4 > > Oh, also some builds of crypt_blowfish (and of affected systems/apps) > for PowerPC are probably unaffected, because char is typically unsigned > there (unless overridden in compiler flags for compatibility with more > typical systems). > > Once again, my apologies for the mess. > > Alexander >
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