CVSS 3.1 Score 6.5 of 10 (medium)


Published Aug 4, 2023
Updated: Aug 11, 2023
CWE ID 287


CVE-2023-38691 is a vulnerability in the matrix-appservice-bridge library, affecting versions 4.0.0 to 8.1.2 and 9.0.1. It allows a malicious Matrix server to impersonate users when using the provisioning API by using a foreign user's MXID in an OpenID exchange. The library does not properly check the servername part of the 'sub' parameter, allowing a bad actor to spin up a server on any domain and respond with a 'sub' parameter according to the targeted user they want to act as. The resulting token can then be used for unauthorized provisioning requests. Versions 8.1.2 and 9.0.1 have been patched, but as a workaround, it is recommended to disable the provisioning API altogether. This vulnerability has a base severity rating of MEDIUM, with LOW privileges required and HIGH confidentiality impact, making it potentially dangerous for organizations using affected products.


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