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GHSA-35g4-qx3c-vjhx

MediumCVSS 6.5 / 10
Published Jun 21, 2021·Last modified Mar 13, 2026
Affected Components(0)

No affected components available

Description

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.

Risk Scores
Base Score
6.5

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information.

Threat Intelligence
6.0

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
0.94%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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