CVE-2015-8985

Vulnerability

The pop_fail_stack function in the GNU C Library (glibc) contains an assertion failure that can be triggered during processing of extended regular expressions. This vulnerability affects glibc versions prior to 2.28 [2]. The bug is located in the regex engine and can be reached when an application compiles or executes a crafted regular expression using functions such as regcomp or regexec.

Exploitation

An attacker can exploit this vulnerability by providing a specially crafted extended regular expression to an application that uses glibc's regex functions. No authentication or special privileges are required if the application accepts user-supplied regex patterns. The crafted input causes an assertion failure in pop_fail_stack, leading to an immediate application crash.

Impact

Successful exploitation results in a denial of service (DoS) condition: the affected application crashes due to the assertion failure. There is no evidence of information disclosure, privilege escalation, or remote code execution. The crash is limited to the process handling the malicious regex.

Mitigation

The issue is fixed in glibc version 2.28 and later [2]. Users should upgrade their glibc installation to the latest version. No known workaround exists for unpatched systems. The Gentoo security advisory GLSA 201908-06 recommends upgrading to >=sys-libs/glibc-2.28-r4 [2].