Description
Matrix-appservice-bridge is the bridging service for the Matrix communication program's application services. In versions 2.6.0 and earlier, 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 malicious admin of a bridged room can repoint the traffic to a different room without the new room being aware. Versions 2.6.1 and greater are patched. As a workaround, disabling the automatic room upgrade handling can be done by removing the `roomUpgradeOpts` key from the `Bridge` class options.
Published: 2021-06-16
Score: 6.5 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
EUVD EUVD EUVD-2021-1248 Matrix-appservice-bridge is the bridging service for the Matrix communication program's application services. In versions 2.6.0 and earlier, 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 malicious admin of a bridged room can repoint the traffic to a different room without the new room being aware. Versions 2.6.1 and greater are patched. As a workaround, disabling the automatic room upgrade handling can be done by removing the `roomUpgradeOpts` key from the `Bridge` class options.
Github GHSA Github GHSA GHSA-35g4-qx3c-vjhx Automatic room upgrade handling can be used maliciously to bridge a room non-consentually
History

Tue, 24 Feb 2026 17:00:00 +0000

Type Values Removed Values Added
Title Automatic room upgrade handling can be used maliciously to bridge a room non-consentually Automatic room upgrade handling can be used maliciously to bridge a room non-consentually

Subscriptions

Matrix Matrix-appservice-bridge
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2024-08-03T23:25:31.074Z

Reserved: 2021-05-12T00:00:00.000Z

Link: CVE-2021-32659

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Modified

Published: 2021-06-16T19:15:38.830

Modified: 2024-11-21T06:07:28.667

Link: CVE-2021-32659

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses