CVE-2023-38691

matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to provisioning APIs

Description

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.

Category

5.0
CVSS
Severity: Medium
CVSS 3.1 •
EPSS 0.06%
Third-Party Advisory github.com
Affected: matrix-org matrix-appservice-bridge
Published at:
Updated at:

References

Link Tags
https://github.com/matrix-org/matrix-appservice-bridge/security/advisories/GHSA-vc7j-h8xg-fv5x third party advisory
https://github.com/matrix-org/matrix-appservice-bridge/commit/4c6723a5e7beda65cdf1ae5dbb882e8beaac8552 patch

Frequently Asked Questions

What is the severity of CVE-2023-38691?
CVE-2023-38691 has been scored as a medium severity vulnerability.
How to fix CVE-2023-38691?
To fix CVE-2023-38691, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2023-38691 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2023-38691 is being actively exploited. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2023-38691?
CVE-2023-38691 affects matrix-org matrix-appservice-bridge.
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