CVE-2016-2513 in Django
Summary
by MITRE
The password hasher in contrib/auth/hashers.py in Django before 1.8.10 and 1.9.x before 1.9.3 allows remote attackers to enumerate users via a timing attack involving login requests.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability described in CVE-2016-2513 represents a critical timing attack flaw within the Django web application framework's authentication system. This issue affects versions prior to 1.8.10 and 1.9.3, specifically targeting the password hashing implementation in the contrib/auth/hashers.py module. The vulnerability stems from the inconsistent response times generated during authentication attempts, which can be exploited by malicious actors to determine whether a given username exists within the system. Attackers can leverage this timing information to perform user enumeration attacks, effectively mapping out valid user accounts without requiring legitimate credentials.
The technical flaw manifests through the predictable timing behavior of the authentication process when handling login requests. When Django processes a login attempt with an invalid username, the system typically responds with a different timing pattern compared to when it processes a valid username. This differential timing occurs because the password verification process includes a cryptographic hash comparison that takes varying amounts of time depending on whether the username exists in the database. The attacker can measure these response time differences and use statistical analysis to determine which usernames are valid, essentially bypassing traditional authentication mechanisms through side-channel attacks.
This vulnerability directly impacts the confidentiality and integrity of authentication systems by enabling unauthorized user enumeration, which can serve as a precursor to more sophisticated attacks such as credential stuffing, brute force attempts, or social engineering campaigns. The operational impact extends beyond simple account discovery, as it undermines the fundamental security assumptions of the authentication layer. Organizations using affected Django versions face significant risk of account compromise, particularly when combined with other reconnaissance activities that can identify valid user accounts. The vulnerability is particularly dangerous in environments where user enumeration could lead to targeted attacks against specific individuals or groups, potentially resulting in unauthorized access to sensitive systems and data.
The security implications of CVE-2016-2513 align with CWE-203, which addresses "Observable Timing Discrepancy" in security systems, and can be categorized under ATT&CK technique T1078 for Valid Accounts and T1562 for Impair Defenses. Organizations should immediately upgrade to Django versions 1.8.10 or 1.9.3 and later to address this vulnerability. Additional mitigations include implementing rate limiting on authentication attempts, using constant-time comparison functions for password verification, and deploying intrusion detection systems to monitor for suspicious timing patterns. The fix implemented by Django developers involved ensuring that the authentication process takes consistent time regardless of whether the username exists, thereby eliminating the timing side-channel that enabled the attack.