CVE-2014-8639 in Firefox
Summary
by MITRE
Mozilla Firefox before 35.0, Firefox ESR 31.x before 31.4, Thunderbird before 31.4, and SeaMonkey before 2.32 do not properly interpret Set-Cookie headers within responses that have a 407 (aka Proxy Authentication Required) status code, which allows remote HTTP proxy servers to conduct session fixation attacks by providing a cookie name that corresponds to the session cookie of the origin server.
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Analysis
by VulDB Data Team • 03/02/2022
This vulnerability exists in Mozilla Firefox and related applications across multiple versions where the software fails to properly handle Set-Cookie headers in HTTP responses with 407 status codes. The flaw occurs when a proxy server returns a 407 Proxy Authentication Required response containing Set-Cookie headers that match the session cookie names used by the origin server. This misinterpretation allows malicious proxy servers to inject cookies that can hijack user sessions and conduct session fixation attacks.
The technical implementation of this vulnerability stems from improper cookie handling logic within the HTTP response processing pipeline. When Firefox receives a 407 response from a proxy server, it should not process Set-Cookie headers as they indicate authentication requirements rather than legitimate session management. However, the affected versions fail to distinguish between proxy authentication responses and regular web server responses, leading to the acceptance and storage of potentially malicious cookies.
From an operational perspective, this vulnerability creates significant security risks for users who rely on proxy servers for internet access. Attackers can exploit this weakness by positioning themselves as malicious proxy servers between users and target websites. The session fixation attack allows attackers to establish a known session identifier that can be used to hijack legitimate user sessions once authentication is completed. This effectively bypasses session management controls and can lead to unauthorized access to user accounts and sensitive data.
The vulnerability maps to CWE-613, which addresses inadequate session management, and aligns with ATT&CK technique T1190 for exploit public-facing application. Organizations using affected versions of Firefox, Thunderbird, or SeaMonkey face potential compromise when users access the internet through untrusted proxy servers. The attack vector requires the user to be behind a malicious proxy that can intercept and modify HTTP responses, making it particularly dangerous in corporate environments or public networks where proxy usage is common.
Mitigation strategies include immediate upgrade to patched versions of the affected software, implementation of network monitoring to detect unusual proxy behavior, and deployment of web application firewalls that can filter malicious Set-Cookie headers in 407 responses. Additionally, organizations should consider implementing strict proxy policies and educating users about the risks of connecting through untrusted proxy servers. Network administrators should also configure proxy server logging to detect potential exploitation attempts and implement proper certificate validation to prevent man-in-the-middle attacks that could leverage this vulnerability.