CVE-2009-0801 in Squid
Summary
by MITRE
Squid, when transparent interception mode is enabled, uses the HTTP Host header to determine the remote endpoint, which allows remote attackers to bypass access controls for Flash, Java, Silverlight, and probably other technologies, and possibly communicate with restricted intranet sites, via a crafted web page that causes a client to send HTTP requests with a modified Host header.
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Analysis
by VulDB Data Team • 07/26/2024
The vulnerability described in CVE-2009-0801 represents a critical security flaw in the Squid proxy server software that manifests when operating in transparent interception mode. This configuration allows Squid to intercept and process HTTP traffic without requiring client-side configuration changes, making it particularly useful in network environments where centralized proxy control is desired. The flaw specifically exploits the proxy server's reliance on the HTTP Host header to determine the destination endpoint for requests, creating a pathway for malicious actors to circumvent established access controls and security policies.
The technical implementation of this vulnerability stems from Squid's transparent proxy mode behavior where it intercepts HTTP traffic based on the destination IP address and port, but then uses the Host header value to establish the actual target server for the request. When a client makes a request to a web page that contains maliciously crafted content, particularly embedded Flash, Java, or Silverlight objects, the attacker can manipulate the Host header to point to internal network resources that would normally be restricted. This occurs because Squid does not properly validate or sanitize the Host header values when operating in transparent mode, allowing arbitrary host names to be processed as legitimate destinations.
The operational impact of this vulnerability extends beyond simple access control bypass to potentially enable internal network reconnaissance and exploitation. Attackers can construct malicious web pages that, when viewed by users behind the Squid proxy, cause the browser to send HTTP requests with modified Host headers that target internal systems. This capability allows for communication with restricted intranet sites that should normally be inaccessible from external networks, effectively creating a tunnel through the proxy's security controls. The vulnerability affects multiple technologies including Flash, Java, and Silverlight because these technologies often make HTTP requests to external resources that can be manipulated through the Host header, creating multiple attack vectors for exploitation.
This vulnerability aligns with CWE-284, which addresses improper access control issues, and represents a significant weakness in the proxy server's authorization mechanisms. The attack pattern follows principles outlined in the ATT&CK framework under T1071.001 for application layer protocol usage and T1046 for network service discovery. Organizations using Squid in transparent mode should consider implementing additional security controls such as Host header validation, explicit access control lists for internal resources, and network segmentation to prevent unauthorized access. The recommended mitigations include disabling transparent interception mode when possible, implementing strict Host header validation rules, configuring proper access controls for internal resources, and monitoring proxy logs for unusual Host header patterns that might indicate exploitation attempts.
The broader implications of this vulnerability highlight the importance of proper input validation in proxy server implementations and demonstrate how seemingly benign HTTP header processing can create significant security risks. Organizations must understand that transparent proxy configurations, while convenient for network management, introduce additional attack surface that requires careful security consideration. The vulnerability also underscores the need for comprehensive security testing of proxy server configurations and the importance of maintaining up-to-date software to prevent exploitation of known weaknesses in network infrastructure components.