CVE-2025-61672

MEDIUM

5.3

CVSS v4

Description

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.

CWE-1287Improper Validation of Specified Type of Input

How to fix

Remediation Available

matrix-synapseDebian

Fixed in:1.139.2-1CVE-2025-61672

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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v4 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredLow

User InteractionNone

Impact

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Exploit Intelligence

0.47%probability of exploitation in 30 days

39thpercentile

Low risk: more likely to be exploited than 39% of all known CVEs.

References

Other references6

Related Vulnerabilities

Other CWE-1287 (Improper Validation of Specified Type of Input) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-4879	Critical	9.8	100%	KEV	-
CVE-2022-31007	Medium	4.9	27%	-	Fix
CVE-2024-6298	Critical	10.0	19%	-	-
CVE-2026-25639	High	7.5	2.7%	-	Fix
CVE-2026-59680	High	8.0	2.3%	-	-
CVE-2021-43802	Critical	9.9	2.0%	-	Fix

Common questions

How do I fix CVE-2025-61672?

Upgrade matrix-synapse on debian unstable to 1.139.2-1 or later.

Is CVE-2025-61672 being actively exploited?

Not that we know of. CVE-2025-61672 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.47% is the estimated probability that it will be exploited in the next 30 days. That is higher than 39% of all scored CVEs.

How severe is CVE-2025-61672?

CVE-2025-61672 has a CVSS v4 base score of 5.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2025-61672 affect?

Published advisories record a fix for matrix-synapse (Debian). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-17.