Automatic room upgrade handling can be used maliciously to bridge a room non-consentually

Exploitation

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

CVSS

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

EPSS

• CVE-2021-32659: 0.94% estimated exploitation activity in the next 30 days; percentile 60.86 (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.

Impact If a bridge has room upgrade handling turned on in the configuration (the roomUpgradeOpts key when instantiating a new Bridge instance.), any m.room.tombstone event it encounters will be used to unbridge the current room and bridge into the target room. However, the target room m.room.create event is not checked to verify if the predecessor field contains the previous room. This means that any mailcious admin of a bridged room can repoint the traffic to a different room without the new room being aware. Patches Versions 2.6.1 and greater are patched. Workarounds Disabling the automatic room upgrade handling can be done by removing the roomUpgradeOpts key from the Bridge class options. References The issue is patched by https://github.com/matrix-org/matrix-appservice-bridge/pull/330 For more information] If you have any questions or comments about this advisory, email us at security@matrix.org.

Published by the source

21 Jun 2021, 17:09 UTC

Last modified by the source

8 Jul 2026, 06:29 UTC

Source last checked

26 Oct 2026, 12:21 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-35g4-qx3c-vjhx

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-35g4-qx3c-vjhx

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# Patch Next advisory brief: CVE-2021-32659

Advisory: Automatic room upgrade handling can be used maliciously to bridge a room non-consentually
IDs: CVE-2021-32659, GHSA-35g4-qx3c-vjhx
Record: https://patchnext.com/advisories/cve-2021-32659 (revision 2, source checked 26 Oct 2026, 12:21 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: matrix-appservice-bridge 2.6.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm matrix-appservice-bridge: affected < 2.6.1; fixed in 2.6.1

## Suggested inspection (read-only)
- `npm ls matrix-appservice-bridge --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## 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-appservice-bridge.
- 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-35g4-qx3c-vjhx (OSV record GHSA-35g4-qx3c-vjhx lists affected ranges: npm matrix-appservice-bridge >=0 <2.6.1 (fixed))
- Verified: https://github.com/advisories/GHSA-35g4-qx3c-vjhx (GitHub-reviewed advisory GHSA-35g4-qx3c-vjhx lists affected ranges: npm matrix-appservice-bridge >=0 <2.6.1)

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