CVE-2007-4727 in lighttpd
Summary
by MITRE
Buffer overflow in the fcgi_env_add function in mod_proxy_backend_fastcgi.c in the mod_fastcgi extension in lighttpd before 1.4.18 allows remote attackers to overwrite arbitrary CGI variables and execute arbitrary code via an HTTP request with a long content length, as demonstrated by overwriting the SCRIPT_FILENAME variable, aka a "header overflow."
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Analysis
by VulDB Data Team • 03/15/2021
The vulnerability described in CVE-2007-4727 represents a critical buffer overflow flaw within the lighttpd web server's mod_fastcgi extension. This issue affects versions prior to 1.4.18 and specifically targets the fcgi_env_add function located in mod_proxy_backend_fastcgi.c. The flaw enables remote attackers to manipulate CGI environment variables through carefully crafted HTTP requests, creating a pathway for arbitrary code execution. The vulnerability manifests when an attacker sends an HTTP request containing an excessively long content length parameter, which triggers the buffer overflow condition in the FastCGI backend processing module. This particular weakness falls under the CWE-121 buffer overflow category, which is classified as a critical vulnerability in software security practices. The attack vector leverages the HTTP protocol's header processing mechanisms to exploit memory corruption in the web server's FastCGI handling code.
The technical implementation of this vulnerability exploits the improper bounds checking within the fcgi_env_add function, where the application fails to validate the length of incoming data before copying it into fixed-size buffers. When an attacker crafts a request with an extended content length value, the application processes this data without adequate size validation, leading to memory overwrite conditions. The specific demonstration of this exploit involves overwriting the SCRIPT_FILENAME CGI variable, which is a critical environment variable used by FastCGI applications to determine which script to execute. This variable manipulation creates a direct path for code execution since the web server will attempt to execute whatever path is specified in the compromised SCRIPT_FILENAME variable. The vulnerability's impact is amplified by the fact that FastCGI applications typically execute with elevated privileges, potentially allowing attackers to gain system-level access. This weakness aligns with ATT&CK technique T1190 for exploiting vulnerabilities in web applications and T1059 for executing commands through compromised web servers.
The operational consequences of this vulnerability extend beyond simple code execution to encompass complete system compromise and data exfiltration capabilities. Attackers can leverage this flaw to establish persistent access to web servers running vulnerable versions of lighttpd, potentially using the compromised server as a launch point for further attacks within a network infrastructure. The vulnerability's remote exploitability means that attackers do not require physical access or prior authentication to exploit the flaw, making it particularly dangerous for publicly accessible web servers. Organizations running lighttpd versions prior to 1.4.18 face significant risk of unauthorized access, data breaches, and potential system compromise. The attack can be automated and executed at scale, making it attractive to threat actors seeking to exploit multiple systems simultaneously. The vulnerability also demonstrates the importance of proper input validation and memory management practices in web server software, as inadequate bounds checking can lead to severe security implications.
Mitigation strategies for CVE-2007-4727 require immediate patching of lighttpd installations to version 1.4.18 or later, which contains the necessary fixes for the buffer overflow condition. System administrators should also implement network-level protections such as intrusion detection systems that monitor for suspicious HTTP request patterns, particularly those with unusually long content length headers. Additional defensive measures include configuring web application firewalls to filter out malformed HTTP requests and implementing strict input validation policies for all HTTP headers. Organizations should conduct comprehensive vulnerability assessments to identify all systems running vulnerable versions of lighttpd and ensure that proper security updates are applied across their infrastructure. The vulnerability highlights the necessity of maintaining up-to-date software components and implementing robust security monitoring practices to detect and respond to exploitation attempts. Regular security audits and penetration testing can help identify similar buffer overflow vulnerabilities in other web server components or applications that may be susceptible to similar attacks.