CVE-2019-25025 in activerecord-session_store
Summary
by MITRE • 03/05/2021
The activerecord-session_store (aka Active Record Session Store) component through 1.1.3 for Ruby on Rails does not use a constant-time approach when delivering information about whether a guessed session ID is valid. Consequently, remote attackers can leverage timing discrepancies to achieve a correct guess in a relatively short amount of time. This is a related issue to CVE-2019-16782.
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Analysis
by VulDB Data Team • 03/28/2021
The CVE-2019-25025 vulnerability affects the Active Record Session Store component within Ruby on Rails applications, specifically versions through 1.1.3. This flaw represents a timing attack vulnerability that exploits the non-constant-time comparison operations used during session ID validation processes. The vulnerability stems from the component's failure to implement consistent time responses when validating session identifiers, creating measurable timing differences that can be exploited by remote attackers to determine valid session IDs through systematic guessing attempts.
The technical implementation of this vulnerability lies in how the session store component handles session ID validation. When a session ID is submitted for validation, the system should perform comparisons in constant time regardless of whether the ID matches a valid session or not. However, the Active Record Session Store component uses variable-time comparison algorithms that reveal timing information through the response duration. This timing discrepancy occurs because valid session IDs trigger different execution paths than invalid ones, resulting in measurable delays that attackers can exploit through statistical analysis and repeated requests.
The operational impact of this vulnerability is significant for applications relying on Rails session management, as it enables credential stuffing and session hijacking attacks. Attackers can systematically guess session IDs and use the timing variations to distinguish between valid and invalid attempts, dramatically reducing the time required to discover legitimate session tokens. This weakness directly relates to the broader category of timing attacks that have been documented in cybersecurity literature and is classified under CWE-203 Information Exposure Through Timing Discrepancies. The vulnerability essentially provides an automated method for attackers to bypass session security measures that would normally require extensive brute force efforts.
The security implications extend beyond simple session guessing, as this vulnerability can be leveraged in conjunction with other attack vectors to compromise application availability and user privacy. Attackers can combine this timing-based approach with other reconnaissance techniques to map session structures and potentially identify valid user sessions within the application. This vulnerability aligns with ATT&CK technique T1212 Exploitation for Credential Access, where adversaries exploit application-level weaknesses to obtain valid credentials or session tokens. The impact is particularly severe in applications handling sensitive user data, as successful exploitation can lead to unauthorized access to user accounts and potential data breaches.
Mitigation strategies for CVE-2019-25025 include upgrading to Rails version 5.2.3 or later, where the Active Record Session Store has been patched to implement constant-time comparison operations. Organizations should also consider implementing additional security controls such as rate limiting and request monitoring to detect and prevent systematic timing-based attacks. The fix addresses the root cause by ensuring all session validation operations execute in constant time regardless of input values, eliminating the timing discrepancies that made the vulnerability exploitable. Security teams should also conduct thorough testing to verify that session management components properly implement constant-time operations and monitor for similar timing vulnerabilities in other application components.