CVE-2009-1836 in Firefox
Summary
by MITRE
Mozilla Firefox before 3.0.11, Thunderbird before 2.0.0.22, and SeaMonkey before 1.1.17 use the HTTP Host header to determine the context of a document provided in a non-200 CONNECT response from a proxy server, which allows man-in-the-middle attackers to execute arbitrary web script by modifying this CONNECT response, aka an "SSL tampering" attack.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 09/06/2019
This vulnerability represents a critical security flaw in Mozilla's web browser suite that affects the handling of HTTP CONNECT responses during SSL/TLS connections through proxy servers. The issue stems from how Firefox, Thunderbird, and SeaMonkey interpret the HTTP Host header when processing non-200 CONNECT responses from proxy infrastructure, creating an avenue for sophisticated man-in-the-middle attacks that can compromise secure communications. The vulnerability specifically targets the SSL/TLS connection establishment process where proxy servers relay requests between clients and destination servers, making it particularly dangerous in enterprise environments where proxy infrastructure is commonly deployed.
The technical flaw manifests when a proxy server returns a non-200 HTTP response code during an SSL connection attempt, but includes a Host header in the response that contains malicious content or points to an unintended destination. The affected browsers incorrectly trust this Host header information to determine the document context and SSL certificate validation context, essentially allowing attackers to manipulate the SSL connection establishment process. This behavior creates a scenario where an attacker positioned between the client and proxy server can modify the CONNECT response to include a malicious Host header, causing the browser to establish an SSL connection to an attacker-controlled server rather than the legitimate destination. The vulnerability falls under CWE-345 Insufficient Verification of Data Authenticity, specifically related to trust relationships in network communications and certificate validation.
The operational impact of this vulnerability is severe as it enables attackers to perform SSL tampering attacks that can intercept and modify encrypted communications without detection. An attacker can successfully impersonate legitimate websites and potentially capture sensitive data transmitted over SSL connections, including login credentials, personal information, and business data. The attack requires the victim to be behind a proxy server that the attacker can influence or control, but this is common in corporate networks and public WiFi environments. The vulnerability affects not just web browsing but also email communications through Thunderbird, making it particularly dangerous for organizations that rely on secure email protocols. According to ATT&CK framework, this vulnerability maps to T1573.002 (Encrypted Channel) and T1071.004 (Application Layer Protocol: DNS), as it exploits the trust model in application layer protocols and enables unauthorized access to encrypted channels.
The mitigation strategy involves updating to the patched versions of the affected software products, with Mozilla releasing versions 3.0.11 for Firefox, 2.0.0.22 for Thunderbird, and 1.1.17 for SeaMonkey. Organizations should also implement network monitoring to detect unusual proxy behavior and consider deploying additional security controls such as SSL inspection appliances that can validate the authenticity of SSL connections. Network administrators should ensure that proxy servers properly validate and sanitize HTTP headers, particularly Host headers, in CONNECT responses to prevent malicious modifications from propagating to client browsers. The vulnerability highlights the importance of proper input validation and trust model implementation in network security protocols, as it demonstrates how seemingly benign header processing can create critical security weaknesses in SSL/TLS implementations.