CVE-2025-61672Network attack vector

Federation disruption via unvalidated device-key uploads

Published Oct 8, 2025 · Updated Oct 8, 2025

Improper device-key validation in Element Synapse before 1.138.3 and 1.139.0 allows remote authenticated users to disrupt federation. The POST /_matrix/client/v3/keys/upload handler persists device-key objects without validating their structure or ensuring embedded user and device identifiers match the authenticated session. An account registered on the homeserver can upload malformed keys that unpredictably break outbound federation to other homeservers, without reported confidentiality impact.

CVSS severity5.3
Medium
EPSS probability0.47%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper device-key validation in Element Synapse before 1.138.3 and 1.139.0 allows remote authenticated users to disrupt federation. The POST /_matrix/client/v3/keys/upload handler persists device-key objects without validating their structure or ensuring embedded user and device identifiers match the authenticated session. An account registered on the homeserver can upload malformed keys that unpredictably break outbound federation to other homeservers, without reported confidentiality impact.

The record

CVE
CVE-2025-61672
Published
Oct 8, 2025
Updated
Oct 8, 2025
Vendor
Element HQ
Product
Synapse
Classifications
CWE-1287, T1499
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 8, 2025CVE publishedPublication date reported by the CVE source.
  2. Oct 8, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.138.3
  2. Affected versionversion== 1.139.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Element HQ · Synapseversion=< 1.138.3; version== 1.139.0

Published CVSS scores

5.3GitHub CNACVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1287Improper Validation of Specified Type of Input
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo