CVE-2004-0488 in HTTP Server
Summary
by MITRE
Stack-based buffer overflow in the ssl_util_uuencode_binary function in ssl_util.c for Apache mod_ssl, when mod_ssl is configured to trust the issuing CA, may allow remote attackers to execute arbitrary code via a client certificate with a long subject DN.
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Analysis
by VulDB Data Team • 07/12/2025
The vulnerability described in CVE-2004-0488 represents a critical stack-based buffer overflow within the Apache mod_ssl module that affects the ssl_util_uuencode_binary function in ssl_util.c. This flaw occurs specifically when Apache servers are configured to trust the issuing Certificate Authority, creating a scenario where remote attackers can exploit the vulnerability through maliciously crafted client certificates. The buffer overflow vulnerability stems from insufficient input validation and bounds checking within the function responsible for encoding binary data during SSL certificate processing. When a client presents a certificate with an unusually long subject distinguished name, the function fails to properly validate the length of the input data, leading to memory corruption on the stack. This memory corruption can be leveraged by attackers to overwrite adjacent memory locations, potentially allowing for arbitrary code execution with the privileges of the Apache process. The vulnerability is particularly concerning because it operates at the SSL/TLS layer where certificate validation occurs, making it accessible to any attacker who can establish an SSL connection to the vulnerable server. The impact extends beyond simple privilege escalation as the exploitation can lead to complete server compromise, data exfiltration, and potential lateral movement within the network infrastructure.
The technical nature of this vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflows occurring in stack memory regions where insufficient bounds checking allows attackers to overwrite adjacent memory. The flaw demonstrates characteristics consistent with the attack pattern described in the MITRE ATT&CK framework under T1055 Process Injection, as successful exploitation would likely involve injecting malicious code into the Apache process memory space. The vulnerability is particularly dangerous because it operates in a server context where the Apache process typically runs with elevated privileges, potentially allowing attackers to gain root access or at minimum full control over the web server. The specific conditions required for exploitation include the presence of mod_ssl module, configuration enabling CA trust, and the ability to present a client certificate with an excessively long subject DN. This makes the vulnerability particularly relevant in environments where mutual SSL authentication is implemented, as is common in enterprise security architectures and secure web applications.
The operational impact of CVE-2004-0488 extends far beyond immediate code execution capabilities, as successful exploitation can result in complete compromise of the affected web server infrastructure. Organizations running vulnerable Apache servers with mod_ssl configured for CA trust face significant risk of data breaches, service disruption, and potential use as a foothold for broader network infiltration. The vulnerability's remote exploitability means that attackers do not require physical access or network proximity to the target server, making it particularly dangerous in publicly accessible web environments. The exploitation process would likely involve crafting a specially formatted client certificate with an extended subject distinguished name that exceeds the allocated buffer space, causing the stack overflow to occur during certificate validation. This type of vulnerability also creates challenges for incident response teams, as the exploitation may not immediately produce obvious signs of compromise, allowing attackers to maintain persistence within the environment for extended periods. The vulnerability's age and widespread presence in Apache installations at the time of discovery meant that many organizations were potentially exposed to this risk for extended periods, highlighting the importance of timely security patch management and vulnerability assessment procedures.
Mitigation strategies for CVE-2004-0488 should focus on both immediate remediation and long-term security improvements to prevent similar vulnerabilities from occurring in the future. The most effective immediate solution involves applying the relevant security patches provided by the Apache Software Foundation, which would include updating the mod_ssl module to versions that properly validate input lengths and prevent buffer overflows. Organizations should also consider implementing certificate validation policies that limit the maximum length of subject distinguished names accepted from client certificates, creating additional defense-in-depth measures. Network segmentation and access controls should be implemented to restrict access to SSL-enabled services where possible, reducing the attack surface available to potential attackers. Additionally, organizations should conduct thorough vulnerability assessments to identify other potential buffer overflow vulnerabilities in their Apache installations and related modules. The implementation of intrusion detection systems capable of identifying suspicious certificate validation patterns and monitoring for signs of exploitation attempts can provide early warning capabilities. Regular security audits and code reviews focusing on memory management practices and input validation procedures should be implemented to prevent similar vulnerabilities from being introduced in future code releases, aligning with security best practices outlined in industry standards such as NIST SP 800-53 and ISO 27001. The vulnerability also underscores the importance of maintaining current security awareness and implementing comprehensive patch management procedures across all server infrastructure components.