CVE-2023-38691
MediumCVSS 5.0Exploitation Probability (EPSS)
Low risk30th percentile - higher than 30% of all known CVEs
Summary
In versions 4.0.0 to 8.1.1, the matrix-appservice-bridge library allows a malicious Matrix server to use a foreign user's MXID in an OpenID exchange, enabling impersonation of users via the provisioning API.
Risk Assessment
This vulnerability could lead to unauthorized access to user resources and data, posing a significant security risk to the organization.
Recommendation
It is recommended to upgrade to versions 8.1.2 or 9.0.1, which contain patches. Alternatively, the provisioning API can be temporarily disabled.
Original NVD description (English source)
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.