CVE-2018-12423 in Synapse
Summary
by MITRE
In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.
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Analysis
by VulDB Data Team • 03/27/2023
The vulnerability identified as CVE-2018-12423 affects the Matrix Synapse distributed instant messaging server software and represents a significant authorization flaw that allows unauthorized users to gain administrative control over chat rooms. This issue exists in versions prior to 0.31.2 of the Synapse server implementation, creating a persistent security weakness that can be exploited by malicious actors who are not legitimate room participants. The vulnerability specifically targets the room management and permission system within the Matrix protocol implementation, where the absence of proper power level event enforcement creates an exploitable condition.
The technical flaw stems from the absence of proper validation mechanisms when no m.room.power_levels event exists within a room's state. In the Matrix protocol, power levels define user permissions and administrative capabilities within rooms, with the m.room.power_levels event serving as the authoritative source for determining who can perform specific actions such as kicking users, changing room settings, or modifying messages. When this event is missing or improperly handled, the system defaults to a vulnerable state where unauthorized users can manipulate room parameters and assume control over room operations. This condition aligns with CWE-284 Access Control Bypass, where inadequate access control mechanisms allow unauthorized entities to perform privileged operations.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it enables complete room hijacking and potential disruption of communication services. An attacker can exploit this weakness to take over any room where the power_levels event has not been properly established, allowing them to modify room configurations, ban legitimate users, or inject malicious content into conversations. This type of attack directly violates the principle of least privilege and can be classified under ATT&CK technique T1078 Valid Accounts, where adversaries leverage legitimate credentials or system weaknesses to gain unauthorized access to resources. The vulnerability is particularly concerning in environments where Synapse servers host sensitive communications or serve as critical infrastructure for collaborative workspaces.
Mitigation strategies for CVE-2018-12423 primarily involve upgrading to Synapse version 0.31.2 or later, which includes proper enforcement of power level events and robust validation of room state management. System administrators should also implement comprehensive monitoring of room state changes and ensure that all rooms maintain proper power level configurations. The fix addresses the underlying issue by enforcing default power level settings when no explicit m.room.power_levels event exists, preventing unauthorized users from assuming control over room operations. Additionally, organizations should conduct regular security assessments of their Matrix implementations and ensure proper access control policies are in place to minimize the attack surface and maintain the integrity of collaborative communication environments.