When matrix-nio receives forwarded room keys, the receiver doesn't check if it requested the key from the forwarder

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.6 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

EPSS

• CVE-2022-39254: 0.68% estimated exploitation activity in the next 30 days; percentile 52.37 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

When matrix-nio before 0.20 requests a room key from our devices, it correctly accepts key forwards only if they are a response to a previous request. However, it doesn't check that the device that responded matches the device the key was requested from. This allows a malicious homeserver to insert room keys of questionable validity into the key store in some situations, potentially assisting in an impersonation attack. For more information If you have any questions or comments about this advisory, e-mail us at poljar@termina.org.uk.

Published by the source

30 Sep 2022, 22:56 UTC

Last modified by the source

7 Jul 2026, 11:56 UTC

Source last checked

26 Oct 2026, 13:12 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-w4pr-4vjg-hffh

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-w4pr-4vjg-hffh

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# Patch Next advisory brief: CVE-2022-39254

Advisory: When matrix-nio receives forwarded room keys, the receiver doesn't check if it requested the key from the forwarder
IDs: CVE-2022-39254, GHSA-w4pr-4vjg-hffh
Record: https://patchnext.com/advisories/cve-2022-39254 (revision 2, source checked 26 Oct 2026, 13:12 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: matrix-nio 0.20. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI matrix-nio: affected < 0.20; fixed in 0.20

## Suggested inspection (read-only)
- `python -m pip show matrix-nio`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on matrix-nio.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-w4pr-4vjg-hffh (OSV record GHSA-w4pr-4vjg-hffh lists affected ranges: PyPI matrix-nio >=0 <0.20 (fixed))
- Verified: https://github.com/advisories/GHSA-w4pr-4vjg-hffh (GitHub-reviewed advisory GHSA-w4pr-4vjg-hffh lists affected ranges: PyPI matrix-nio >=0 <0.20)

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