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Vulnerabilities

Security incident · CVE-2025-61672

Synapse is an open source Matrix homeserver implementation.

Published Oct 8, 2025 · catalog updated Oct 15, 2025 · Synapse is an open

Last checked Oct 26, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2025-61672. EPSS is 0.47%. Act only if a listed version of Synapse is an open is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Synapse is an open).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
Medium5.3
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.47%
Remediation
Advisory link
Affected products
vendor element-hq synapse = 1.139.0

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 1.13

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor element-hq synapse = 1.139.0= 1.139.0

How to fix CVE-2025-61672

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2025-61672. EPSS is 0.47%. Act only if a listed version of Synapse is an open is installed.

Which versions are affected?

Compare what you have installed with element-hq synapse = 1.139.0 = 1.139.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.47%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 8, 2025 · EUVD

    Detected

    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.

  2. Oct 15, 2025 · EUVD

    Updated

    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.

Sources

  • CVE.orgVulnerability recordCVE-2025-61672

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2025-61672

    30-day exploitation probability 0.47%

    first.org
  • EUVDVulnerability recordEUVD-2025-33305

    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

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Oct 26, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • CVE.orgOct 23, 2026
  • FIRST EPSSOct 23, 2026
  • EUVDOct 23, 2026