CVE-2003-0542 in HTTP Server
Summary
by MITRE
Multiple stack-based buffer overflows in (1) mod_alias and (2) mod_rewrite for Apache before 1.3.29 allow attackers to create configuration files to cause a denial of service (crash) or execute arbitrary code via a regular expression with more than 9 captures.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability identified as CVE-2003-0542 represents a critical security flaw affecting Apache httpd versions prior to 1.3.29, specifically within the mod_alias and mod_rewrite modules. This issue stems from improper handling of regular expressions in Apache configuration files, creating conditions where malicious input can trigger stack-based buffer overflows. The vulnerability manifests when attackers craft configuration directives containing regular expressions with more than nine capture groups, exploiting fundamental memory management flaws in the Apache server's processing mechanisms.
The technical implementation of this vulnerability involves the exploitation of stack buffer overflows in the Apache server's module handling code. When Apache processes configuration files containing regular expressions with excessive capture groups, the server's internal buffer management fails to properly validate the number of captures, leading to memory corruption. This memory corruption occurs during the parsing and compilation phases of regular expressions, where the server allocates stack space based on assumptions about capture group counts. The CWE-121 classification applies here as the vulnerability involves stack-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent stack memory. The flaw specifically affects the mod_alias and mod_rewrite modules, which are fundamental components for URL manipulation and aliasing within Apache's configuration system.
The operational impact of this vulnerability extends beyond simple denial of service to encompass full arbitrary code execution capabilities. An attacker who successfully exploits this vulnerability can cause Apache processes to crash, leading to denial of service conditions, or more critically, execute arbitrary code with the privileges of the Apache user. This represents a severe privilege escalation risk in environments where Apache runs with elevated permissions. The vulnerability's exploitability is enhanced by the fact that it can be triggered through configuration file modifications, making it particularly dangerous in environments where configuration management is automated or where attackers can influence server configuration through various attack vectors. The ATT&CK framework categorizes this as a privilege escalation technique, specifically mapping to T1068 (Local Privilege Escalation) and T1566 (Phishing for Information) when attackers leverage configuration file manipulation to establish persistent access.
Mitigation strategies for CVE-2003-0542 focus primarily on immediate version upgrades to Apache 1.3.29 or later, which contain the necessary patches to address the buffer overflow conditions. Organizations should implement comprehensive configuration management practices to prevent unauthorized modifications to Apache configuration files, particularly those involving mod_alias and mod_rewrite directives. Network segmentation and access controls should be enforced to limit who can modify server configuration files. Additionally, implementing intrusion detection systems that monitor for suspicious regular expression patterns in configuration files can provide early warning capabilities. Security teams should conduct thorough audits of existing Apache configurations to identify and remove any regular expressions with excessive capture groups, while also establishing automated scanning processes to prevent future introduction of vulnerable patterns. The vulnerability's remediation requires not just patching the software but also implementing defensive measures around configuration file integrity and access controls to prevent exploitation through configuration manipulation.