CVE-2003-0899 in thttpd
Summary
by MITRE
Buffer overflow in defang in libhttpd.c for thttpd 2.21 to 2.23b1 allows remote attackers to execute arbitrary code via requests that contain < or > characters, which trigger the overflow when the characters are expanded to "<" and ">" sequences.
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Analysis
by VulDB Data Team • 10/13/2024
The vulnerability described in CVE-2003-0899 represents a critical buffer overflow flaw within the thttpd web server software version 2.21 through 2.23b1. This issue resides in the defang function located within the libhttpd.c source file, which processes HTTP requests and handles character sequences that are commonly used in web applications. The flaw specifically manifests when the web server encounters requests containing the less than '<' or greater than '>' characters, which are fundamental elements in HTML and XML parsing. These characters trigger a buffer overflow condition when the software attempts to expand these sequences into their full "<" and ">" representations during request processing.
The technical implementation of this vulnerability stems from inadequate input validation and buffer management within the defang function. When thttpd processes incoming HTTP requests containing these special characters, the software fails to properly bounds-check the destination buffers before copying expanded character sequences. This oversight creates a classic buffer overflow condition where data written to memory locations beyond the allocated buffer space can overwrite adjacent memory regions. The vulnerability is particularly dangerous because it allows remote attackers to execute arbitrary code with the privileges of the thttpd process, which typically runs with elevated system permissions. Attackers can craft malicious HTTP requests that contain carefully constructed sequences of '<' and '>' characters, causing the buffer overflow to overwrite critical memory structures including return addresses on the stack.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with a pathway to compromise entire web servers and potentially gain unauthorized access to underlying systems. The attack vector is particularly concerning because it requires minimal sophistication to exploit, relying only on standard HTTP request construction with common HTML characters. This vulnerability affects a wide range of web servers running thttpd versions within the specified range, making it a significant threat to organizations that have not updated their web server software. The buffer overflow can be leveraged to cause denial of service conditions, data corruption, or complete system compromise, depending on the attacker's objectives and the specific system configuration. The vulnerability also demonstrates poor software security practices related to input handling and memory management, which aligns with CWE-121, which specifically addresses stack-based buffer overflow conditions.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security improvements. The most effective immediate solution involves upgrading to thttpd versions that contain patches for this specific buffer overflow issue, as newer versions implement proper bounds checking and input validation. Organizations should also implement network-level protections such as web application firewalls and intrusion prevention systems that can detect and block malicious requests containing suspicious character sequences. Additional defensive measures include disabling unnecessary web server features, implementing strict input validation at the application level, and conducting regular security assessments of web server configurations. The vulnerability serves as a reminder of the importance of following secure coding practices such as those outlined in the OWASP Secure Coding Practices and aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as successful exploitation would likely involve executing malicious code through the compromised web server. System administrators should also consider implementing monitoring and logging mechanisms to detect unusual patterns of requests that might indicate exploitation attempts, and establish incident response procedures to handle potential compromises.