CVE-2016-1939 in Firefox
Summary
by MITRE
Mozilla Firefox before 44.0 stores cookies with names containing vertical tab characters, which allows remote attackers to obtain sensitive information by reading HTTP Cookie headers. NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-7208.
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Analysis
by VulDB Data Team • 07/06/2022
The vulnerability described in CVE-2016-1939 represents a critical security flaw in Mozilla Firefox versions prior to 44.0 that stems from an incomplete remediation of a previously identified issue. This weakness specifically affects how the browser handles cookie storage and transmission, creating a pathway for remote attackers to extract sensitive information from HTTP cookie headers. The vulnerability is particularly concerning because it builds upon the foundation of CVE-2015-7208, indicating a pattern of insufficiently addressed security concerns that persist across software updates.
The technical flaw manifests when Firefox encounters cookie names containing vertical tab characters, which are represented as ASCII character 0x0B. These characters are typically used for formatting purposes in text processing but are not standard in cookie name specifications. The browser's cookie handling mechanism fails to properly sanitize or validate cookie names containing such characters, leading to improper storage and subsequent transmission in HTTP headers. This behavior creates a situation where attackers can craft malicious cookie names that contain vertical tab characters, which then get processed and transmitted in a manner that could expose sensitive session data or authentication tokens.
From an operational perspective, this vulnerability enables remote attackers to perform information disclosure attacks by exploiting the improper cookie handling behavior. When the browser transmits HTTP headers containing cookies with vertical tab characters, the presence of these special characters can cause unexpected parsing behavior in web servers or intermediate proxies. This parsing inconsistency allows attackers to potentially extract cookie values that should remain confidential, as the vertical tab characters may interfere with standard HTTP header parsing mechanisms and create opportunities for data leakage. The impact extends beyond simple session management, potentially compromising user authentication state and sensitive application data stored in cookies.
The vulnerability aligns with CWE-20, which describes improper input validation, and demonstrates the importance of comprehensive testing for security fixes. Attackers can exploit this weakness through various means including cross-site scripting attacks, where malicious web pages inject cookie names with vertical tab characters, or by manipulating HTTP responses from compromised servers. The ATT&CK framework categorizes this under credential access techniques, specifically targeting the extraction of authentication tokens through web application vulnerabilities. Organizations should prioritize immediate patching of affected Firefox versions and implement monitoring for unusual cookie header patterns in their network traffic analysis systems.
Mitigation strategies should include immediate deployment of Firefox 44.0 or later versions, which contain the complete fix for this vulnerability. Security teams should also implement web application firewalls that can detect and block cookie headers containing non-standard characters, and establish monitoring procedures to identify anomalous cookie handling behavior in web applications. Additionally, organizations should conduct thorough security testing of web applications to ensure they properly handle cookie names with special characters and implement proper input validation mechanisms to prevent similar issues from occurring in other components of their infrastructure. The vulnerability serves as a reminder of the critical importance of comprehensive security testing and the potential for incomplete fixes to create persistent security risks.