CVE-2014-7817

Vulnerability

The wordexp function in the GNU C Library (glibc) prior to the patched versions does not properly enforce the WRDE_NOCMD flag when processing arithmetic expansion inputs of the form $((......)). The backticks within the arithmetic expression are evaluated by a shell even though WRDE_NOCMD is intended to forbid command substitution. This vulnerability affects glibc versions 2.17 and earlier on Red Hat Enterprise Linux 7 [1], versions 2.12 and earlier on Oracle Linux 6 [4], and version 2.21 as described in the CVE. The issue was fixed in glibc trunk on November 19, 2014 [3].

Exploitation

An attacker can exploit this flaw by providing input that includes a specially crafted arithmetic expansion containing backtick-embedded commands, such as $((command)). The attacker does not require authentication or special privileges; they only need to supply this input to an application that calls wordexp() with the WRDE_NOCMD flag. The wordexp() function will then execute the commands inside the backticks, bypassing the intended restriction [3].

Impact

Successful exploitation allows an attacker to execute arbitrary shell commands with the privileges of the process that invoked wordexp(). This can lead to full system compromise if the vulnerable process runs with elevated privileges, such as root. The impact includes arbitrary code execution, data disclosure, and potential denial of service [1][2].

Mitigation

Patches are available from the respective vendors. Red Hat released updated glibc packages (version 2.17-55.el7_0.3) in RHSA-2014-2023 [1]. Oracle released updates for Oracle Linux 7 (glibc-2.17-55.0.4.el7_0.5) in ELSA-2015-0092 [2] and for Oracle Linux 6 (glibc-2.12-1.149.el6_6.4) in ELSA-2015-0016 [4]. Users should apply the appropriate updates as soon as possible. No known workarounds exist; updating glibc is the only mitigation.