element-hq synapse up to 1.138.2/1.139.0 improper validation of specified type of input

Summaryinfo

A vulnerability has been found in element-hq synapse up to 1.138.2/1.139.0 and classified as problematic. Affected is an unknown function. Performing a manipulation results in improper validation of specified type of input. This vulnerability is known as CVE-2025-61672. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as problematic has been found in element-hq synapse up to 1.138.2/1.139.0. This affects an unknown part. The manipulation with an unknown input leads to a improper validation of specified type of input vulnerability. CWE is classifying the issue as CWE-1287. The product receives input that is expected to be of a certain type, but it does not validate or incorrectly validates that the input is actually of the expected type. This is going to have an impact on integrity, and availability. The summary by CVE is:

Synapse is an open source Matrix homeserver implementation. Lack of validation for device keys in Synapse before 1.138.3 and in Synapse 1.139.0 allow an attacker registered on the victim homeserver to degrade federation functionality, unpredictably breaking outbound federation to other homeservers. The issue is patched in Synapse 1.138.3, 1.138.4, 1.139.1, and 1.139.2. Note that even though 1.138.3 and 1.139.1 fix the vulnerability, they inadvertently introduced an unrelated regression. For this reason, the maintainers of Synapse recommend skipping these releases and upgrading straight to 1.138.4 and 1.139.2.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2025-61672 since 09/29/2025. The exploitability is told to be easy. It is possible to initiate the attack remotely. Neither technical details nor an exploit are publicly available.

Upgrading to version 1.138.3 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch 26aaaf9e48fff80cf67a20c691c75d670034b3c1 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• element-hq

Name

• synapse

Version

• 1.138.0
• 1.138.1
• 1.138.2
• 1.139

License

• open-source

Website

• Product: https://github.com/element-hq/synapse/

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