CVE-2018-12291 in Synapse
Summary
by MITRE
The on_get_missing_events function in handlers/federation.py in Matrix Synapse before 0.31.1 has a security bug in the get_missing_events federation API where event visibility rules were not applied correctly.
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Analysis
by VulDB Data Team • 03/27/2023
The vulnerability identified as CVE-2018-12291 resides within the Matrix Synapse federated messaging server software and represents a critical flaw in the event visibility enforcement mechanism. This security issue affects versions prior to 0.31.1 and specifically targets the on_get_missing_events function located in the handlers/federation.py file. The core problem manifests when the federation API processes requests for missing events, where the system fails to properly enforce room visibility rules that govern which events users should be able to access or retrieve.
The technical flaw stems from improper implementation of access control mechanisms within the federation protocol handling layer. When Matrix Synapse receives requests for missing events from other servers in the federated network, the system should verify that the requesting server has appropriate permissions to access the requested events based on room membership and visibility policies. However, the vulnerability allows malicious actors to bypass these visibility checks, potentially enabling unauthorized access to events that should remain restricted based on room membership or privacy settings. This flaw operates at the protocol level of the Matrix federation API, specifically impacting the get_missing_events endpoint that facilitates event synchronization between federated servers.
The operational impact of this vulnerability extends beyond simple information disclosure, as it fundamentally compromises the privacy and security model of Matrix chat rooms. Attackers could exploit this weakness to access events in rooms they do not belong to, potentially gaining insight into private conversations, sensitive communications, or restricted content within federated Matrix networks. The vulnerability affects all Matrix servers running versions before 0.31.1, making it particularly concerning given the widespread adoption of the Matrix protocol for both personal and enterprise communications. This issue directly violates the principle of least privilege and undermines the fundamental security assumptions of the federated messaging system.
Security mitigations for CVE-2018-12291 primarily involve upgrading to Matrix Synapse version 0.31.1 or later, which contains the necessary patches to properly enforce event visibility rules during federation operations. Organizations should also implement monitoring for unusual federation API activity and consider additional access controls for federation endpoints. The vulnerability aligns with CWE-284, which addresses improper access control, and relates to ATT&CK technique T1071.004 for application layer protocol, as it exploits weaknesses in the federated messaging protocol implementation. Network administrators should also review their federation configurations and ensure proper server-to-server authentication mechanisms are in place to minimize potential exploitation vectors.