CVE-2023-38691

Description

### Impact 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. ### Details The library does not check that the servername part of the `sub` parameter (containing the user's *claimed* MXID) is 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. ### Workarounds Disable the provisioning API. If the bridge does not use the provisioning API, you are not vulnerable.

How to fix CVE-2023-38691

To remediate CVE-2023-38691, upgrade the affected package to a fixed version below.

• —upgrade to 8.1.2 or later

Is CVE-2023-38691 being exploited?

Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.

Affected packages (1)

• >= 4.0.0, < 8.1.2

CVSS scores

References (4)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2023-38691
• PATCHgithub.com/matrix-org/matrix-appservice-bridge
• WEBgithub.com/matrix-org/matrix-appservice-bridge/commit/4c6723a5e7beda65cdf1ae5dbb882e8beaac8552
• WEBgithub.com/matrix-org/matrix-appservice-bridge/security/advisories/GHSA-vc7j-h8xg-fv5x