CVE-2023-38691 json
matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to provisioning APIs
published 2023-08-04 3 y ago modified 2026-09-10 1 mo ago also GHSA-vc7j-h8xg-fv5x , EUVD-2023-2361
- cvss
- 5.0
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.5%
- EPSS 0.5% chance of exploitation in 30 days, percentile 40%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- npm matrix-appservice-bridge 8.1.2, 9.0.1
- matrix matrix-appservice-bridge 8.1.2
CISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 2 y ago
Exploit prediction
0.47% chance of exploitation in the next 30 days, higher than 40% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 5.0 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N |
| NVD | 3.1 | 6.5 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N |
| GitHub | 3.1 | 5.0 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| npm | matrix-appservice-bridge | >=4.0.0, <8.1.2 >=9.0.0, <9.0.1 |
8.1.2 9.0.1 |
Affected products
- matrix-org matrix-appservice-bridge
Classification
- Weakness
-
- CWE-287 Improper Authentication
References
-
github.com
/matrix-org/matrix-appservice-bridge/commit/4c6723a5e7beda65cdf1ae5dbb882e8beaac8552
web, patch
-
github.com
/matrix-org/matrix-appservice-bridge/security/advisories/GHSA-vc7j-h8xg-fv5x
web, third-party-advisory
-
nvd.nist.gov
/vuln/detail/CVE-2023-38691
advisory
-
github.com
/matrix-org/matrix-appservice-bridge
package
Sources
- CVE List CVE-2023-38691
- GitHub Advisory GHSA-vc7j-h8xg-fv5x
- NVD CVE-2023-38691
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