CVE-2012-0883 in HTTP Server
Summary
by MITRE
envvars (aka envvars-std) in the Apache HTTP Server before 2.4.2 places a zero-length directory name in the LD_LIBRARY_PATH, which allows local users to gain privileges via a Trojan horse DSO in the current working directory during execution of apachectl.
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Analysis
by VulDB Data Team • 04/20/2021
The vulnerability identified as CVE-2012-0883 affects the Apache HTTP Server version 2.4.2 and earlier, specifically within the envvars component also known as envvars-std. This flaw represents a classic privilege escalation vector that exploits how the server handles dynamic shared object (DSO) loading through the LD_LIBRARY_PATH environment variable. The vulnerability stems from the improper construction of the library path during the Apache server initialization process, creating a security loophole that local attackers can exploit to execute malicious code with elevated privileges.
The technical root cause of this vulnerability lies in how the envvars script manages the LD_LIBRARY_PATH environment variable. When Apache initializes, it sets up the library path to include various directories where shared libraries are expected to reside. However, in versions prior to 2.4.2, the script incorrectly includes a zero-length directory name within this path. This zero-length entry effectively means that the current working directory is included in the library search path, creating an environment where any shared library placed in the current directory will be loaded before system libraries. This behavior aligns with CWE-427 Uncontrolled Search Path Element, which describes how applications that search for libraries in a predictable order without proper validation can be tricked into loading malicious code from unexpected locations.
The operational impact of this vulnerability is significant for systems running affected Apache versions, particularly those where the apachectl script is executed with elevated privileges. When a local user can manipulate the current working directory from which apachectl is executed, they can place a malicious DSO file in that location. Upon execution of apachectl, the system will load this malicious library instead of the legitimate one, potentially allowing the attacker to execute arbitrary code with the privileges of the Apache process. This creates a privilege escalation scenario where a local user can gain elevated access to the system. The attack vector is particularly concerning because it requires minimal privileges to set up the malicious DSO file, yet can result in full system compromise.
This vulnerability demonstrates the critical importance of proper environment variable handling and library path management in security-sensitive applications. The flaw is categorized under the ATT&CK framework as privilege escalation through environment variable manipulation, specifically leveraging the technique of DLL side-loading or library injection. Organizations should consider implementing strict library path validation and avoiding the inclusion of current working directories in library search paths. The recommended mitigation involves upgrading to Apache HTTP Server version 2.4.2 or later, where this issue has been resolved through proper handling of the LD_LIBRARY_PATH variable. Additionally, system administrators should ensure that the apachectl script is not executed from directories writable by untrusted users, and that proper file permissions are maintained on Apache configuration directories to prevent unauthorized modification of DSO files.