CVE-2004-0700 in mod_ssl
Summary
by MITRE
Format string vulnerability in the mod_proxy hook functions function in ssl_engine_log.c in mod_ssl before 2.8.19 for Apache before 1.3.31 may allow remote attackers to execute arbitrary messages via format string specifiers in certain log messages for HTTPS that are handled by the ssl_log function.
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Analysis
by VulDB Data Team • 07/12/2025
This vulnerability represents a classic format string exploit targeting the Apache web server's mod_ssl module, specifically within the ssl_engine_log.c file's hook functions. The flaw exists in the ssl_log function where user-controllable input from HTTPS requests is processed through format string operations without proper sanitization. Attackers can manipulate log messages containing format specifiers such as %s, %d, or %x, which are then interpreted by the printf family of functions, potentially leading to information disclosure, stack corruption, or arbitrary code execution. The vulnerability affects Apache versions prior to 1.3.31 and mod_ssl versions before 2.8.19, making it particularly dangerous in environments where older Apache installations remain in use.
The technical implementation of this vulnerability stems from improper input validation within the ssl_engine_log.c module where HTTPS request data is logged without adequate sanitization of format string specifiers. When the ssl_log function processes incoming HTTPS requests, it directly incorporates user-supplied data into log messages that are subsequently processed through format string functions. This creates a scenario where an attacker can inject malicious format specifiers into HTTPS request headers, cookies, or other user-controllable data elements that get logged by the ssl_log function. The vulnerability is classified under CWE-134 as "Use of Externally-Controlled Format String" and aligns with ATT&CK technique T1059.007 for command and scripting interpreter execution through format string manipulation.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable full system compromise. Attackers can leverage this flaw to read arbitrary memory locations from the server process, potentially extracting sensitive information such as cryptographic keys, session tokens, or other confidential data stored in memory. In more sophisticated attacks, the format string vulnerability can be exploited to overwrite memory addresses, leading to stack corruption and potential arbitrary code execution. The attack vector is particularly insidious because it operates through normal HTTPS traffic handling, making detection difficult and allowing attackers to remain undetected while performing reconnaissance or executing malicious payloads. The vulnerability affects not just the web server's availability but also its integrity and confidentiality, as demonstrated by the potential for privilege escalation and persistent access to the affected systems.
Mitigation strategies for this vulnerability primarily focus on immediate patching and configuration hardening. Organizations must upgrade to Apache 1.3.31 or later versions along with mod_ssl 2.8.19 or newer to address the core flaw in the ssl_engine_log.c implementation. Beyond patching, administrators should implement input validation measures to sanitize user-controllable data before it reaches logging functions, though this is secondary to the primary remediation approach. Network monitoring solutions should be configured to detect unusual logging patterns or potential format string exploitation attempts. The vulnerability also highlights the importance of following secure coding practices such as using fixed string formats with explicit argument counts rather than allowing user input to control format specifiers. Additionally, organizations should consider implementing intrusion detection systems that can identify the specific patterns associated with format string exploitation attempts and maintain comprehensive logging and monitoring to detect potential exploitation of similar vulnerabilities in other components of the web server stack.