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Fencer Vulns
medium 6.5

CVE-2021-32659 json

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

published 2021-06-16 5 y ago modified 2026-07-08 4 mo ago also GHSA-35g4-qx3c-vjhx , EUVD-2021-1248

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.9%
EPSS 0.9% chance of exploitation in 30 days, percentile 61%
public exploits
0
none known

Summary

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.

Patch / fix

  • npm matrix-appservice-bridge 2.6.1
  • matrix matrix-appservice-bridge 2.6.1
  • matrix-appservice-irc Arch Linux 0.27.0-1

arch linux advisories AVG-2076

Exploit prediction

0.94% chance of exploitation in the next 30 days, higher than 61% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
NVD 3.1 4.9 CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N
NVD 2.0 3.5 AV:N/AC:M/Au:S/C:N/I:P/A:N
GitHub 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
npm matrix-appservice-bridge
<2.6.1
2.6.1

Affected products

  • matrix-org matrix-appservice-bridge

Classification

Weakness
  • CWE-306 Missing Authentication for Critical Functionality

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.