Auth bypass in Matrix Matrix-Appservice-Bridge
CVE-2023-38691
matrix-appservice-bridge provides an API for setting up bridges. Starting in version 4.0.0 and prior to versions 8.1.2 and 9.0.1, a malicious Matrix server can use a foreign user's MXID in an OpenID exchange, allowing a bad actor to impersonate users when using the provisioning API. The library does not check that the servername part of the `sub` parameter (containing the user's *claimed* MXID) is the the same as the servername we are talking to. A malicious actor could spin up a server on any given domain, respond with a `sub` parameter according to the user they want to act as and use the resulting token to perform provisioning requests. Versions 8.1.2 and 9.0.1 contain a patch. As a workaround, disable the provisioning API.
Vulnerability class: Broken Authentication
EPSS: 0.004 (31.3th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.0 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N.
Affected products
- Matrix Matrix-appservice-bridge — versions 9.0.0
- Matrix-org Matrix-appservice-bridge — versions >= 4.0.0, < 8.1.2, = 9.0.0
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Third Party Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
Frequently asked questions
- What is CVE-2023-38691?
- CVE-2023-38691 is a medium-severity vulnerability in Matrix Matrix-Appservice-Bridge, classified under Improper Authentication. CVSS score: 5.0/10. Published 2023-08-04.
- How severe is CVE-2023-38691?
- Medium severity. CVSS v3 base score is 5.0 out of 10.