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

Moderate severity GitHub Reviewed Published Aug 4, 2023 in matrix-org/matrix-appservice-bridge • Updated Nov 7, 2023

Package

npm matrix-appservice-bridge (npm)

Affected versions

>= 4.0.0, < 8.1.2
= 9.0.0

Patched versions

8.1.2
9.0.1

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.

References

@Half-Shot Half-Shot published to matrix-org/matrix-appservice-bridge Aug 4, 2023
Published by the National Vulnerability Database Aug 4, 2023
Published to the GitHub Advisory Database Aug 4, 2023
Reviewed Aug 4, 2023
Last updated Nov 7, 2023

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality
Low
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(28th percentile)

Weaknesses

CVE ID

CVE-2023-38691

GHSA ID

GHSA-vc7j-h8xg-fv5x

Source code

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