CVE-2009-3095 in HTTP Server
Summary
by MITRE
The mod_proxy_ftp module in the Apache HTTP Server allows remote attackers to bypass intended access restrictions and send arbitrary commands to an FTP server via vectors related to the embedding of these commands in the Authorization HTTP header, as demonstrated by a certain module in VulnDisco Pack Professional 8.11.
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Analysis
by VulDB Data Team • 08/22/2021
The CVE-2009-3095 vulnerability resides within the mod_proxy_ftp module of the Apache HTTP Server, representing a critical authorization bypass flaw that fundamentally undermines the security controls designed to protect FTP server communications. This vulnerability specifically targets the way Apache handles authentication headers when acting as a proxy for FTP connections, creating a pathway for remote attackers to circumvent intended access controls and execute unauthorized commands against backend FTP servers. The flaw manifests through the improper handling of the Authorization HTTP header, where embedded FTP commands are processed without adequate validation or sanitization, allowing malicious actors to inject arbitrary FTP commands that get forwarded to the target FTP server.
The technical exploitation of this vulnerability occurs when an attacker crafts a specially formatted Authorization header that contains FTP commands intended for the backend server. This technique leverages the proxy functionality of mod_proxy_ftp, which is designed to forward HTTP requests to FTP servers while maintaining authentication. However, the module fails to properly validate or sanitize the command content within the Authorization header, enabling command injection attacks that can result in unauthorized access to FTP resources, data exfiltration, or even complete compromise of the underlying FTP server infrastructure. The vulnerability is particularly dangerous because it operates at the HTTP protocol level, making it difficult to detect through traditional network monitoring and firewall rules.
The operational impact of CVE-2009-3095 extends beyond simple unauthorized access, as it provides attackers with the capability to perform a wide range of malicious activities against the targeted FTP infrastructure. Attackers can leverage this vulnerability to execute arbitrary FTP commands such as LIST, RETR, STOR, and other administrative functions, potentially leading to data loss, unauthorized file modifications, or the establishment of persistent access points within the network. The vulnerability also enables attackers to bypass authentication mechanisms entirely, as the injected commands are processed with the privileges of the proxy user account, potentially escalating privileges and gaining access to additional resources within the FTP server environment. This represents a significant compromise of the principle of least privilege and can result in widespread data exposure across multiple systems.
Organizations affected by this vulnerability should implement immediate mitigations including disabling the mod_proxy_ftp module when it is not essential for operations, applying the latest security patches from Apache, and implementing strict network segmentation to limit access to FTP proxy functionality. Network administrators should also deploy intrusion detection systems capable of monitoring for suspicious Authorization header patterns and implement comprehensive logging of proxy activities for forensic analysis. The vulnerability aligns with CWE-77 and CWE-20 categories, specifically addressing command injection flaws and improper input validation issues, while also mapping to ATT&CK techniques related to proxy usage and command execution. Regular security assessments and vulnerability scanning should be conducted to identify any remaining instances of the mod_proxy_ftp module in production environments, as the vulnerability can remain undetected for extended periods due to its subtle nature and the complexity of monitoring HTTP proxy operations.