Date: Tue, 2 Oct 2012 13:42:44 -0500 From: Raphael Geissert <geissert@...ian.org> To: Kurt Seifried <kseifried@...hat.com> Cc: oss-security@...ts.openwall.com Subject: Re: CVE request - mcrypt buffer overflow flaw Kurt, I think at least one more CVE id needs to be assigned: On Saturday 15 September 2012 19:22:06 Raphael Geissert wrote: > On Tuesday 11 September 2012 10:19:38 Eygene Ryabinkin wrote: > > Unfortunately, mcrypt's check_file_head() in combination with > > decrypt_general() is a bit worse: it allows to overwrite up to 50 > > bytes of stack buffers from decrypt_general(), namely local_algorithm, > > local_mode, local_keymode. And in some curcumstances to overwrite > > even 2-3 extra bytes (not more, since buf will contain '\0'), though > > it is not very much controllable path. > > > > The problem is that no length checks are done in combos > > read_until_null/strcpy. Function read_until_null() allows for up to > > 100 bytes to be read and it won't NUL-terminate the buffer, so strcpy > > can do perform access even further (read from tmp_buf and writes to > > the said buffers; but this is the uncontrolled way I was talking > > about). > > > > The modified PoC is at > > > > http://codelabs.ru/security/mcrypt/poc-cve-2012-4409.py > > > > With it I was able to overwrite the salt_size@...rypt_general() > > and to trigger the call to malloc() for the chunk of 0x42424242 bytes > > via _mcrypt_malloc() that lead to bus error because of subsequent > > memmove(): > [...] > > > I wasn't yet able to smash the stack of decrypt_general(), because > > BUFFER_SIZE is 1024 and tmp_buf prevents me to reach the top of the > > stack frame (provided that compiler won't rearrange local variables), > > so I was not able to go past it. Thus it looks like a temporary > > memory consumption/DoS. > > Another week, another couple of patches. One makes it use strncpy and > forces a NUL on the last byte of local_algorithm, local_mode, and > local_keymode. Their values are checked later on, so it seems safe to > pass unvalidated data. > The size of the buffers is hard-coded to avoid making many changes to the > code. I think this needs a separate id, since fixes were released by Fedora and Debian referencing CVE-2012-4409 but only for the original report. Eygene's followup issues have been fixed in Debian without referencing a CVE id. > Once those issues were fixed I noticed that salt_size is not initialized > if the salt flag is not set. The result is an inconditional call to > malloc, with an uninitialized int as argument. This can lead to a > non-attacker-controlled memory consumption DoS in most cases. > It makes me think nobody actually ever used it without a salt. I've no strong opinion on whether this deserves an id. Cheers, -- Raphael Geissert - Debian Developer www.debian.org - get.debian.net
Powered by blists - more mailing lists
Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.