Date: Tue, 16 Aug 2016 15:34:54 +0530 From: Huzaifa Sidhpurwala <huzaifas@...hat.com> To: oss-security@...ts.openwall.com Subject: cracklib: Stack-based buffer overflow when parsing large GECOS field Hi All, A security flaw was reported to us by CSG Labs, details as follows: A stack-based overflow was found in the way cracklib, a library used to stop users from choosing easy to guess passwords, handled large GECOS field in the /etc/passwd file. When an application compiled against the cracklib libary, such as "passwd" is used to parse the GECOS field, it could cause the application to crash or execute arbitary code with the permissions of the user running such an application. To trigger the flaw, you need a specially-crafted "long" GECOS field, which can be done by a local user on the system. The attacker then needs to run some utility which uses cracklib to process this long GECOS field on the system. (such as "passwd" application which runs suid root) All versions of the cracklib library shipped with Red Hat Enterprise Linux are compiled with FORTIFY_SOURCE, which detects the buffer-overflow and aborts the application safely. Therefore the maximum impact of this flaw is application crash. However, there may be other applications, distributions which dont compile cracklib with FORTIFY_SOURCE, and this can lead to easy code exec or even privsec. A proposed patch is available at: https://bugzilla.redhat.com/attachment.cgi?id=1188599 This flaw was assigned CVE-2016-6318 and it was previously disclosed via linux-distros mailing list. -- Huzaifa Sidhpurwala / Red Hat Product Security Team
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