Auth bypass in Matrix Matrix-Appservice-Bridge
CVE-2021-32659
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.
Vulnerability class: Broken Authentication
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.009 (59.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 59th percentile — 59.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000
Affected products
- Matrix Matrix-Appservice-Bridge
- Matrix-Org Matrix-Appservice-Bridge — versions < 2.6.1
Weakness classification (CWE)
References
- github.com/matrix-org/matrix-appservice-bridge/security/advisories/GHSA-35g4-qx… (Third Party Advisory, Mitigation)
- github.com/matrix-org/matrix-appservice-bridge/commit/b69e745584a34fcfd858df33e… (Patch, Third Party Advisory)
- github.com/matrix-org/matrix-appservice-bridge/releases/tag/2.6.1 (Patch, Third Party Advisory)
Frequently asked questions
- What is CVE-2021-32659?
- CVE-2021-32659 is a medium-severity vulnerability in Matrix Matrix-Appservice-Bridge, classified under Missing Authentication for Critical Function. CVSS score: 6.5/10. Published 2021-06-16.
- How severe is CVE-2021-32659?
- Medium severity. CVSS v3 base score is 6.5 out of 10.