CVE-2018-21264 in Mattermost Server
Summary
by MITRE
An issue was discovered in Mattermost Server before 4.7.0, 4.6.2, and 4.5.2. It did not enforce the expiration date of a SAML response.
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Analysis
by VulDB Data Team • 10/26/2020
The vulnerability identified as CVE-2018-21264 represents a critical authentication weakness in Mattermost Server versions prior to 4.7.0, 4.6.2, and 4.5.2. This flaw specifically affects the Single Sign-On implementation through Security Assertion Markup Language which is commonly used in enterprise environments for centralized authentication management. The issue stems from the server's failure to properly validate the expiration timestamp embedded within SAML response documents, creating a potential security vector that could be exploited by malicious actors.
The technical flaw manifests in the SAML authentication flow where Mattermost servers accept SAML responses without verifying their temporal validity. SAML responses contain a NotOnOrAfter attribute that defines when the assertion becomes invalid, typically set to prevent replay attacks and ensure timely authentication. When this validation mechanism is bypassed, attackers can potentially reuse valid SAML assertions beyond their intended expiration period, effectively extending the validity of compromised authentication tokens indefinitely. This vulnerability directly maps to CWE-347, which addresses the lack of proper validation of cryptographic signatures and time-based constraints in authentication protocols.
The operational impact of this vulnerability extends beyond simple authentication bypass scenarios. Attackers who gain access to valid SAML responses could maintain persistent access to Mattermost environments long after the original session should have expired, potentially leading to extended periods of unauthorized access. This creates significant risk for organizations relying on SAML-based authentication for their communication platforms, particularly those with sensitive data or compliance requirements. The vulnerability essentially undermines the fundamental security principle of time-bound authentication tokens that are essential for protecting against session replay attacks and maintaining proper access controls.
Organizations using affected Mattermost versions should immediately implement mitigations including upgrading to the patched versions 4.7.0, 4.6.2, or 4.5.2 where the SAML response expiration validation has been properly implemented. Additionally, security teams should conduct comprehensive audits of their SAML configurations and monitor for any suspicious authentication patterns that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under credential access and defense evasion techniques, as it enables attackers to maintain access while potentially avoiding detection mechanisms that rely on proper session management. Network monitoring should include inspection of SAML traffic to identify any anomalous behavior that might indicate attempts to exploit the time validation bypass, and organizations should consider implementing additional authentication controls such as multi-factor authentication to provide defense-in-depth against potential exploitation of this vulnerability.