CVE-2025-61672: Matrix synapse Synapse's Invalid Device Keys Degrade Vulnerability

MODERATE
Advisory Identifier: GHSA-fh66-fcv5-jjfr
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CWE-1287
Published
Advisory Summary

CVE-2025-61672 is a MODERATE synapse's invalid device keys degrade vulnerability (CWE-1287: Improper Validation of Specified Type of Input) affecting Matrix synapse libraries in the PyPI ecosystem. The issue involves synapse's invalid device keys degrade federation functionality. Remediation is available by upgrading affected packages to version 1.138.3, 1.139.1.

CVE-2025-61672 at a Glance

CVE Identifier CVE-2025-61672
GHSA Identifier GHSA-fh66-fcv5-jjfr
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-1287: Improper Validation of Specified Type of Input
Affected Product Matrix synapse
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2025-61672

To remediate this vulnerability, upgrade all affected Matrix synapse dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

matrix-synapse fixed: 1.138.3 
pip install matrix-synapse>=1.138.3
matrix-synapse fixed: 1.139.1 
pip install matrix-synapse>=1.139.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show matrix-synapse

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2025-61672, inspect your installed packages using pip:

pip show matrix-synapse

Analyze the terminal output to locate any version of Matrix synapse in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.138.3), your application is affected.

Note: The pip show matrix-synapse command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1287: Improper Validation of Specified Type of Input, where 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. In Matrix synapse, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact 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. ### Patches 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, it is recommend to skip these releases and upgrading straight to 1.138.4 and 1.139.2. ### Workarounds The vulnerability can only be exploited by users registered on the victim homeserver.

CVE-2025-61672 Affected Matrix synapse Versions

2 component(s)
Fixed Versions:
1.138.31.139.1
Product / Package Ecosystem Affected Versions Fixed Version
matrix-synapse
pypi/matrix-synapse
PyPI
< 1.138.3
1.138.3
matrix-synapse
pypi/matrix-synapse
PyPI
≥ 1.139.0rc2
< 1.139.1
1.139.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/element-hq/synapse/security/advisories/GHSA-fh66-fcv5-jjfr
NVD — CVE-2025-61672 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-61672
Matrix synapse Source Repository REPOSITORY
https://github.com/element-hq/synapse/pull/17097
Security Fix Commit FIX COMMIT
https://github.com/element-hq/synapse/commit/26aaaf9e48fff80cf67a20c691c75d670034b3c1
Security Fix Commit FIX COMMIT
https://github.com/element-hq/synapse/commit/7069636c2d6d1ef2022287addf3ed8b919ef2740
Matrix synapse Source Repository REPOSITORY
https://github.com/element-hq/synapse
Matrix synapse Release RELEASE
https://github.com/element-hq/synapse/releases/tag/v1.138.3
Matrix synapse Release RELEASE
https://github.com/element-hq/synapse/releases/tag/v1.138.4
Matrix synapse Release RELEASE
https://github.com/element-hq/synapse/releases/tag/v1.139.1
Matrix synapse Release RELEASE
https://github.com/element-hq/synapse/releases/tag/v1.139.2

Frequently Asked Questions

What is CVE-2025-61672?
CVE-2025-61672 is a security vulnerability in Matrix synapse involving Synapse's invalid device keys degrade federation functionality under CWE-1287: Improper Validation of Specified Type of Input.
Which Matrix synapse versions are affected?
Affected versions include releases prior to 1.138.3, 1.139.1 across affected packages: matrix-synapse.
What version fixes CVE-2025-61672?
Upgrading to 1.138.3, 1.139.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is matrix-synapse affected?
Yes, matrix-synapse is affected in releases prior to 1.138.3, 1.139.1. Upgrade your dependency to 1.138.3, 1.139.1 or later.
What CWE is associated with CVE-2025-61672?
CVE-2025-61672 is classified under CWE-1287: Improper Validation of Specified Type of Input (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.).
How can I check PyPI dependencies for CVE-2025-61672?
Run the dependency tree command: 'pip show matrix-synapse'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-fh66-fcv5-jjfr",
  "modified" : "2025-10-08T17:51:02Z",
  "published" : "2025-10-08T17:51:02Z",
  "aliases" : [ "CVE-2025-61672" ],
  "summary" : "Synapse's invalid device keys degrade federation functionality",
  "details" : "### Impact\n\nLack 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. \n\n### Patches\n\nPatched in Synapse 1.138.3, 1.138.4, 1.139.1, and 1.139.2.\n\nNote that even though 1.138.3 and 1.139.1 fix the vulnerability, they inadvertently introduced an unrelated regression. For this reason, it is recommend to skip these releases and upgrading straight to 1.138.4 and 1.139.2.\n\n### Workarounds\n\nThe vulnerability can only be exploited by users registered on the victim homeserver.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
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  }, {
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    "url" : "https://github.com/element-hq/synapse/pull/17097"
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    "url" : "https://github.com/element-hq/synapse"
  }, {
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  }, {
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  }, {
    "type" : "WEB",
    "url" : "https://github.com/element-hq/synapse/releases/tag/v1.139.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1287" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-10-08T17:51:02Z",
    "nvd_published_at" : "2025-10-08T15:16:25Z"
  }
}