CVE-2019-18886 in Symfony
Summary
by MITRE
An issue was discovered in Symfony 4.2.0 to 4.2.11 and 4.3.0 to 4.3.7. The ability to enumerate users was possible due to different handling depending on whether the user existed when making unauthorized attempts to use the switch users functionality. This is related to symfony/security.
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Analysis
by VulDB Data Team • 02/26/2024
This vulnerability exists within the Symfony security component and represents a user enumeration flaw that can be exploited by attackers to determine the existence of specific user accounts. The issue affects versions from 4.2.0 through 4.2.11 and 4.3.0 through 4.3.7, where the framework exhibits inconsistent behavior when processing unauthorized switch user requests. The vulnerability stems from the security mechanism's differential response time or error messaging when attempting to switch to non-existent versus existing users, creating a timing or response pattern that can be analyzed by attackers.
The technical implementation of this vulnerability occurs within the switch user functionality of Symfony's security system. When an unauthorized user attempts to switch to another user account, the framework handles the request differently based on whether the target user exists in the system. This inconsistency manifests in different HTTP response codes, error messages, or processing times that can be distinguished by an attacker. The flaw essentially creates a side-channel information leak where the system's behavior reveals information about user account existence without proper authorization checks.
The operational impact of this vulnerability is significant for applications utilizing Symfony's security features, particularly those with user management capabilities. Attackers can systematically enumerate valid user accounts by making repeated requests to the switch user endpoint and observing the response differences. This enumeration capability enables more targeted attacks including brute force attempts, credential stuffing, or social engineering campaigns that leverage knowledge of valid user accounts. The vulnerability essentially undermines the principle of least privilege by providing unauthorized access to user account information.
This vulnerability maps to CWE-203: Information Exposure Through Discrepancy and aligns with ATT&CK technique T1087.001: Account Discovery - Local Account. The inconsistent error handling creates an information disclosure channel that violates security best practices for defensive programming. Organizations should implement proper error handling that provides uniform responses regardless of user existence, ensuring that all authentication attempts return consistent error messages or status codes to prevent information leakage.
The recommended mitigation strategies include upgrading to patched versions of Symfony where the inconsistency has been resolved, implementing rate limiting on switch user functionality, and ensuring that all authentication endpoints return uniform responses to prevent timing attacks. Additionally, organizations should consider implementing proper access controls and monitoring for suspicious authentication patterns that could indicate enumeration attempts. Security teams should also review their application's error handling practices to ensure that information disclosure vulnerabilities are not present in other components of the system.
The vulnerability demonstrates the importance of consistent error handling in security-sensitive applications and highlights how seemingly minor implementation details can create significant security risks. Proper security design requires that all authentication and authorization mechanisms behave consistently to prevent attackers from gaining intelligence about system internals through differential responses. Organizations should conduct regular security reviews of their authentication flows and implement automated testing to identify similar information disclosure vulnerabilities in their applications.