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
EPSS: 0.009 (57.2th percentile) — read the EPSS interpretation.
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.
Affected products
- Matrix Matrix-appservice-bridge
- Matrix-org Matrix-appservice-bridge — versions < 2.6.1
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Third Party Advisory, Mitigation)
- security-advisories@github.com (Patch, Third Party Advisory, x_refsource_MISC)
- security-advisories@github.com (Patch, Third Party Advisory, x_refsource_MISC)
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.