CVE-2004-0747 in HTTP Server
Summary
by MITRE
Buffer overflow in Apache 2.0.50 and earlier allows local users to gain apache privileges via a .htaccess file that causes the overflow during expansion of environment variables.
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Analysis
by VulDB Data Team • 07/11/2025
The vulnerability identified as CVE-2004-0747 represents a critical buffer overflow flaw within the Apache HTTP Server version 2.0.50 and earlier releases. This security issue stems from improper handling of environment variable expansion within the .htaccess configuration files, creating a pathway for local attackers to escalate their privileges to the apache user level. The flaw exists in the server's processing logic where the system fails to properly validate the length of expanded environment variables, leading to memory corruption that can be exploited for privilege escalation.
The technical implementation of this vulnerability occurs during the parsing and expansion of environment variables within .htaccess files, which are per-directory configuration files that can override server-wide settings. When Apache processes a maliciously crafted .htaccess file containing oversized environment variable expansions, the buffer overflow occurs in the memory management routines responsible for handling these variable expansions. This type of vulnerability maps directly to CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The attack vector requires local access to the system, as the vulnerability cannot be exploited remotely through network connections.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with the ability to execute arbitrary code with elevated privileges. Once an attacker successfully exploits this vulnerability, they can gain full control over the Apache web server process and potentially access all files and resources accessible to the apache user account. This includes the ability to read sensitive configuration files, modify web content, access database connections, and potentially establish persistence mechanisms within the web server environment. The vulnerability affects systems where local users have the ability to write .htaccess files or modify existing ones, which is common in shared hosting environments or when administrators grant insufficient permissions.
Mitigation strategies for CVE-2004-0747 primarily involve immediate patching of affected Apache installations to versions 2.0.51 and later, which contain the necessary fixes for the buffer overflow condition. System administrators should also implement strict file permissions and access controls to prevent unauthorized users from creating or modifying .htaccess files in web directories. The principle of least privilege should be enforced by ensuring that the Apache service runs with minimal required permissions and that no local user accounts have unnecessary write access to web server directories. Additionally, regular security audits should be conducted to verify that no malicious .htaccess files have been introduced into the system, and intrusion detection systems should be configured to monitor for suspicious file modification activities. This vulnerability aligns with ATT&CK technique T1059.007 for command and script interpreter execution, as the privilege escalation could enable attackers to execute arbitrary commands through the web server process. Organizations should also consider implementing file integrity monitoring solutions to detect unauthorized modifications to configuration files and maintain comprehensive system logging to track access patterns that might indicate exploitation attempts.