CVE-2020-6824 in Firefox
Summary
by MITRE
Initially, a user opens a Private Browsing Window and generates a password for a site, then closes the Private Browsing Window but leaves Firefox open. Subsequently, if the user had opened a new Private Browsing Window, revisited the same site, and generated a new password - the generated passwords would have been identical, rather than independent. This vulnerability affects Firefox < 75.
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Analysis
by VulDB Data Team • 05/06/2025
This vulnerability represents a critical cryptographic flaw in Firefox's password management system that undermines the fundamental security assumptions of private browsing sessions. The issue stems from improper isolation between private and regular browsing contexts, where the password generation mechanism fails to maintain distinct cryptographic state when transitioning between different browsing sessions. When users initiate password creation within a private browsing window and subsequently close that window while keeping Firefox running, the application incorrectly maintains certain state information that persists across subsequent private browsing sessions. This cross-contamination of session data creates a scenario where identical passwords are generated for the same website across different private browsing contexts, effectively breaking the expected security boundary that private browsing is designed to enforce.
The technical implementation flaw lies in Firefox's handling of password generation entropy and session state management. When a user closes a private browsing window but keeps the main Firefox application open, the browser should completely reset all private session data including password generation seeds and cryptographic contexts. However, the vulnerability allows certain internal state variables to persist, causing the password generator to use the same seed or initialization vector across multiple sessions. This behavior directly violates the principle of cryptographic independence where each password generation should utilize fresh, unpredictable entropy to ensure uniqueness. The vulnerability specifically affects Firefox versions prior to 75, indicating that the issue was present in the password management subsystem for an extended period and likely exploited by threat actors who understood the session persistence behavior.
The operational impact of this vulnerability extends beyond simple password duplication to represent a significant compromise of user privacy and security. When identical passwords are generated for the same website across different private browsing sessions, it creates a pattern that can be exploited by attackers to correlate user activities across different browsing contexts. This undermines the core purpose of private browsing windows which are designed to provide complete isolation from regular browsing sessions, including protection against session tracking and password correlation attacks. The vulnerability creates a persistent attack surface where an adversary could potentially use the predictable password generation to infer user behavior patterns or target specific users based on their browsing history. From an attacker's perspective, this represents a sophisticated technique for bypassing privacy protections, as demonstrated in the attack pattern where users might unknowingly create predictable password sequences that reveal information about their browsing habits and online activities.
This vulnerability aligns with several cybersecurity frameworks and threat modeling approaches, including the weakness described in CWE-327 (Use of a Broken or Risky Cryptographic Algorithm) and the attack pattern documented in MITRE ATT&CK framework under T1566 (Phishing) and T1531 (Account Access Removal). The issue particularly relates to the concept of session management weakness where proper isolation between different browsing contexts is violated, creating predictable cryptographic outputs that can be exploited by malicious actors. Security professionals should consider this vulnerability when assessing browser security configurations and implementing privacy controls, as it demonstrates how seemingly minor implementation details in cryptographic systems can create significant security risks. The remediation requires proper session isolation and state management that ensures complete entropy separation between private and regular browsing contexts, preventing the persistence of cryptographic state across different user sessions. Organizations should prioritize updating Firefox installations to version 75 or later to address this vulnerability and ensure that their users maintain proper privacy protections when utilizing private browsing features.