CVE-2019-5885 in Synapse
Summary
by MITRE
Matrix Synapse before 0.34.0.1, when the macaroon_secret_key authentication parameter is not set, uses a predictable value to derive a secret key and other secrets which could allow remote attackers to impersonate users.
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Analysis
by VulDB Data Team • 05/18/2020
The vulnerability identified as CVE-2019-5885 affects Matrix Synapse versions prior to 0.34.0.1 and represents a critical security flaw in the authentication mechanism of this decentralized communication platform. Matrix Synapse serves as the reference implementation for Matrix homeservers, enabling secure messaging and collaboration across distributed networks. When the macaroon_secret_key authentication parameter is omitted during configuration, the system defaults to using a predictable value for secret key derivation, creating a significant weakness that adversaries can exploit to compromise user accounts.
This vulnerability stems from the implementation of macaroons as authentication tokens within the Matrix protocol. Macaroons are cryptographic tokens that provide delegation capabilities while maintaining security properties. The flaw occurs when the system fails to properly initialize the macaroon_secret_key parameter, causing it to fall back to a hardcoded or predictable default value. This predictable secret allows remote attackers to compute valid macaroons for any user account, effectively enabling account impersonation and unauthorized access to sensitive communications. The issue directly relates to CWE-320: Use of Hard-coded Cryptographic Keys, which classifies this as a weakness where cryptographic keys are embedded in source code or configuration files in a manner that makes them easily discoverable by attackers.
The operational impact of this vulnerability extends beyond simple account compromise, as it enables sophisticated attacks that can undermine the fundamental security model of the Matrix protocol. Attackers can leverage this weakness to read private messages, send malicious communications, modify user permissions, and potentially gain access to entire rooms and communities within the network. The vulnerability affects the integrity and confidentiality guarantees that users expect from secure messaging systems, as the authentication mechanism becomes effectively useless when the secret key is predictable. This type of flaw particularly impacts organizations relying on Matrix for sensitive communications, as it creates an attack surface that allows unauthorized access to protected information.
Mitigation strategies for CVE-2019-5885 require immediate attention and systematic implementation across all affected Matrix Synapse deployments. The primary remediation involves configuring the macaroon_secret_key parameter with a strong, randomly generated secret value that is unique to each installation. Organizations should also implement proper configuration management practices to ensure that all authentication parameters are correctly set during system deployment. Security teams should conduct thorough audits of their Matrix installations to verify that the macaroon_secret_key parameter is properly configured and that no fallback to default values occurs. The vulnerability demonstrates the importance of following security best practices outlined in the NIST Cybersecurity Framework and aligns with ATT&CK technique T1566.002: Phishing via Service, as it represents a vector that allows attackers to gain unauthorized access through predictable cryptographic weaknesses in authentication systems. Organizations should also consider implementing additional monitoring and detection mechanisms to identify potential exploitation attempts and maintain audit logs of authentication events to track any unauthorized access attempts.