CVE-2021-29431

Name: CVE-2021-29431
Creator: NVD / NIST
Published: 2021-04-15T21:15:17.52+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 1.19%

Last modified Jun 17, 2026

CVE-2021-29431 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. Sydent is a reference Matrix identity server. Sydent can be induced to send HTTP GET requests to internal systems, due to lack of parameter validation or IP address blacklisting. EPSS estimates a 1.19% chance of exploitation in the next 30 days.

Description

Sydent is a reference Matrix identity server. Sydent can be induced to send HTTP GET requests to internal systems, due to lack of parameter validation or IP address blacklisting. It is not possible to exfiltrate data or control request headers, but it might be possible to use the attack to perform an internal port enumeration. This issue has been addressed in in 9e57334, 8936925, 3d531ed, 0f00412. A potential workaround would be to use a firewall to ensure that Sydent cannot reach internal HTTP resources.

Metrics

CVSS 3.1

6.5/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

EPSS Probability

1.19%

64.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Matrix	Sydent	< 2.3.0

References

https://github.com/matrix-org/sydent/commit/0f00412017f25619bc36c264b29ea96808bf310aPatch, Third Party Advisory
https://github.com/matrix-org/sydent/commit/3d531ed50d2fd41ac387f36d44d3fb2c62dd22d3Patch, Third Party Advisory
https://github.com/matrix-org/sydent/commit/8936925f561b0c352c2fa922d5097d7245aad00aPatch, Third Party Advisory
https://github.com/matrix-org/sydent/commit/9e573348d81df8191bbe8c266c01999c9d57cd5fPatch, Third Party Advisory
https://github.com/matrix-org/sydent/releases/tag/v2.3.0Release Notes, Third Party Advisory
https://github.com/matrix-org/sydent/security/advisories/GHSA-9jhm-8m8c-c3f4Patch, Third Party Advisory
https://pypi.org/project/matrix-sydent/Product, Third Party Advisory
https://github.com/matrix-org/sydent/commit/0f00412017f25619bc36c264b29ea96808bf310aPatch, Third Party Advisory
https://github.com/matrix-org/sydent/commit/3d531ed50d2fd41ac387f36d44d3fb2c62dd22d3Patch, Third Party Advisory
https://github.com/matrix-org/sydent/commit/8936925f561b0c352c2fa922d5097d7245aad00aPatch, Third Party Advisory
https://github.com/matrix-org/sydent/commit/9e573348d81df8191bbe8c266c01999c9d57cd5fPatch, Third Party Advisory
https://github.com/matrix-org/sydent/releases/tag/v2.3.0Release Notes, Third Party Advisory
https://github.com/matrix-org/sydent/security/advisories/GHSA-9jhm-8m8c-c3f4Patch, Third Party Advisory
https://pypi.org/project/matrix-sydent/Product, Third Party Advisory

Timeline

Published: Apr 15, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-29431?

How severe is CVE-2021-29431?

CVE-2021-29431 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 1.19% probability of exploitation in the next 30 days.

How do I fix CVE-2021-29431?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-29431?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST