CVE-2018-8023 in Mesos
Summary
by MITRE
Apache Mesos can be configured to require authentication to call the Executor HTTP API using JSON Web Token (JWT). In Apache Mesos versions pre-1.4.2, 1.5.0, 1.5.1, 1.6.0 the comparison of the generated HMAC value against the provided signature in the JWT implementation used is vulnerable to a timing attack because instead of a constant-time string comparison routine a standard `==` operator has been used. A malicious actor can therefore abuse the timing difference of when the JWT validation function returns to reveal the correct HMAC value.
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Analysis
by VulDB Data Team • 03/26/2020
Apache Mesos represents a distributed systems kernel that manages computing resources across clusters of machines, serving as a foundational component for large-scale data processing frameworks. The vulnerability CVE-2018-8023 specifically targets the authentication mechanism within the Executor HTTP API, which relies on JSON Web Tokens for secure access control. This authentication system was designed to protect critical cluster operations by verifying the identity of executors attempting to communicate with the Mesos master through HTTP endpoints. The implementation of JWT-based authentication in Apache Mesos versions prior to 1.4.2, 1.5.0, and 1.5.1 introduced a critical flaw in the cryptographic validation process that fundamentally undermines the security assurances provided by the authentication system.
The technical flaw resides in the comparison operation used during JWT signature validation, where the system employs a standard equality operator `==` instead of implementing a constant-time string comparison routine. This seemingly minor implementation detail creates a significant security vulnerability classified under CWE-203, which specifically addresses "Observable Timing Discrepancy." The timing attack exploits the fact that when comparing strings character by character, the comparison function returns immediately upon detecting a mismatch at any position, creating measurable timing differences. An attacker can systematically probe the system by sending crafted JWT tokens and measuring response times to determine the correct HMAC signature bit by bit, effectively reconstructing the secret key used for token generation. This vulnerability directly maps to ATT&CK technique T1212, which describes "Exploitation for Credential Access" through timing-based attacks.
The operational impact of this vulnerability extends beyond simple authentication bypass, as it provides attackers with the capability to forge valid JWT tokens for the Executor HTTP API. This access could enable malicious actors to execute arbitrary code within the cluster, manipulate task execution, or gain unauthorized access to sensitive cluster information. The vulnerability affects the fundamental integrity of the authentication system, potentially allowing attackers to escalate privileges and compromise the entire Mesos cluster. Organizations using vulnerable versions of Apache Mesos face significant risk as the timing attack can be performed remotely without requiring privileged access or complex exploitation techniques. The attack is particularly concerning because it can be executed systematically and does not require specialized tools beyond standard network monitoring capabilities.
Mitigation strategies for CVE-2018-8023 primarily involve upgrading to Apache Mesos versions 1.4.2, 1.5.0, or 1.5.1, which contain the fixed implementation using constant-time string comparison. Organizations should also consider implementing additional security controls such as network segmentation, monitoring for unusual authentication patterns, and enforcing stricter access controls for the Executor HTTP API endpoints. Security teams should conduct thorough vulnerability assessments to identify systems running vulnerable versions and prioritize remediation efforts based on the criticality of the affected clusters. The fix addresses the root cause by implementing proper constant-time comparison functions that ensure the comparison operation takes the same amount of time regardless of input values, eliminating the timing side-channel that enabled the attack. Organizations should also review their overall security posture and consider implementing additional layers of authentication and authorization to protect against similar vulnerabilities in other components of their distributed systems infrastructure.