CVE-2025-30355 in synapse
Summary
by MITRE • 03/27/2025
Synapse is an open source Matrix homeserver implementation. A malicious server can craft events which, when received, prevent Synapse version up to 1.127.0 from federating with other servers. The vulnerability has been exploited in the wild and has been fixed in Synapse v1.127.1. No known workarounds are available.
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Analysis
by VulDB Data Team • 03/31/2025
The vulnerability identified as CVE-2025-30355 represents a critical flaw in Synapse, an open source Matrix homeserver implementation that serves as the backbone for decentralized messaging infrastructure. This vulnerability specifically targets the federation capabilities of Synapse versions up to 1.127.0, creating a condition where malicious actors can disrupt network connectivity between Matrix servers. The flaw exploits a fundamental aspect of how events are processed and validated within the federation protocol, allowing attackers to craft specially designed events that trigger denial of service conditions. The issue has been confirmed to have been actively exploited in real-world scenarios, demonstrating its practical threat level and the urgency of remediation efforts. The vulnerability impacts the core functionality of Matrix networks by preventing legitimate federation operations, effectively isolating affected servers from the broader Matrix ecosystem.
The technical nature of this vulnerability stems from improper validation of incoming events within the federation processing pipeline of Synapse. When a malicious server crafts events that exploit specific edge cases in the event validation logic, these crafted events cause Synapse to enter an inconsistent state where it cannot properly communicate with other servers in the federation. This occurs because the system fails to properly handle malformed or specially constructed event data that should be rejected during normal validation processes. The flaw likely resides in the event processing code that handles incoming federation data, where insufficient input sanitization or validation logic allows malicious inputs to bypass normal security checks. According to CWE classification, this vulnerability aligns with CWE-20, "Improper Input Validation," as it involves the failure to properly validate incoming data from federated servers. The attack vector operates through the federation protocol where servers exchange events, making this a protocol-level vulnerability rather than a client-side issue.
The operational impact of CVE-2025-30355 extends far beyond simple service disruption, fundamentally compromising the integrity and availability of Matrix networks. Affected servers become isolated from federation, meaning they cannot receive or send messages to other Matrix servers, effectively rendering them useless for their intended purpose of decentralized communication. This isolation creates cascading effects throughout the Matrix ecosystem, as users on affected servers lose connectivity with their contacts on other networks. The vulnerability's exploitation in the wild indicates that threat actors are actively targeting Matrix infrastructure, potentially for purposes ranging from network disruption to more sophisticated attacks that leverage the isolation to perform additional malicious activities. Organizations relying on Matrix for secure communication, collaboration, or messaging services face significant operational risks, as the vulnerability can be exploited to create targeted denial of service conditions against specific servers or entire network segments. The lack of known workarounds forces administrators to immediately upgrade their systems without alternative mitigation strategies.
Mitigation of this vulnerability requires immediate deployment of Synapse version 1.127.1, which contains the necessary patches to address the event validation flaw. System administrators should prioritize upgrading their Synapse installations to prevent exploitation, as no alternative workarounds are available for this specific vulnerability. The patch addresses the core validation logic that was being bypassed by malicious events, restoring proper event processing and federation capabilities. Organizations should conduct thorough testing of the updated version to ensure compatibility with existing configurations and customizations. Security monitoring should be enhanced to detect unusual federation patterns or event processing anomalies that might indicate attempted exploitation. Network administrators should implement additional monitoring for federation connection failures and event processing errors that could indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to techniques involving denial of service through protocol manipulation and network disruption, specifically targeting the federation capabilities that enable Matrix's decentralized architecture. The vulnerability also represents a potential entry point for more sophisticated attacks that could leverage the federation disruption to establish persistent access or perform additional malicious activities within compromised networks.