CVE-2016-4423 in Symfony
Summary
by MITRE
The attemptAuthentication function in Component/Security/Http/Firewall/UsernamePasswordFormAuthenticationListener.php in Symfony before 2.3.41, 2.7.x before 2.7.13, 2.8.x before 2.8.6, and 3.0.x before 3.0.6 does not limit the length of a username stored in a session, which allows remote attackers to cause a denial of service (session storage consumption) via a series of authentication attempts with long, non-existent usernames.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2016-4423 represents a critical denial of service weakness within the Symfony web application framework that affects multiple version branches including 2.3.x, 2.7.x, 2.8.x, and 3.0.x. This flaw resides in the authentication handling mechanism specifically within the UsernamePasswordFormAuthenticationListener component which manages user login processes through HTTP firewalls. The issue stems from insufficient input validation and sanitization practices that allow malicious actors to exploit session storage mechanisms through carefully crafted authentication attempts.
The technical implementation flaw occurs in the attemptAuthentication function where the system fails to impose reasonable limits on username length when storing authentication data in session variables. This particular weakness maps directly to CWE-770, which addresses allocation of resources without proper limits or throttling mechanisms. When attackers submit authentication requests with excessively long usernames, each attempt creates a corresponding session entry that consumes memory and storage resources on the server. The vulnerability operates through a simple yet effective attack pattern where multiple authentication attempts with progressively longer non-existent usernames are executed to rapidly consume available session storage capacity.
The operational impact of this vulnerability extends beyond simple resource exhaustion to potentially compromise the entire application availability. Attackers can systematically consume session storage space through repeated authentication attempts, leading to denial of service conditions where legitimate users cannot establish valid sessions or where the application becomes unresponsive due to memory constraints. This type of attack aligns with ATT&CK technique T1499.004 which covers network denial of service attacks through resource exhaustion. The vulnerability affects session storage mechanisms that are fundamental to web application security and user authentication, making it particularly dangerous in production environments where session management is critical for maintaining application integrity and user access control.
Mitigation strategies for CVE-2016-4423 require immediate implementation of version updates to patched Symfony releases including 2.3.41, 2.7.13, 2.8.6, and 3.0.6 which contain the necessary fixes for username length validation. Organizations should also implement additional defensive measures such as rate limiting authentication attempts, implementing configurable maximum username length restrictions, and monitoring session storage consumption patterns. The fix typically involves adding input validation to ensure that username parameters do not exceed predetermined reasonable limits before being stored in session variables, thereby preventing the exploitation of session storage consumption vulnerabilities while maintaining proper authentication functionality.