CVE-2021-29433: Denial of service (via resource exhaustion) due to improper input validation

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-04-15 · updated 2026-06-17
Weakness: CWE-20

Description

Sydent is a reference Matrix identity server. In Sydent versions 2.2.0 and prior, sissing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion. A patch for the vulnerability is in version 2.3.0. No workarounds are known to exist.

Affected products

matrix-org sydent: before 2.3.0 — fixed in 2.3.0

How to fix

Upgrade to a fixed version: matrix-org sydent 2.3.0. Check the vendor advisory for mitigations.

References

https://github.com/matrix-org/sydent/commit/3175fd358ebc2c310eab7a3dbf296ce2bd54c1da
https://github.com/matrix-org/sydent/security/advisories/GHSA-pw4v-gr34-2553
https://github.com/matrix-org/sydent/commit/3175fd358ebc2c310eab7a3dbf296ce2bd54c1da
https://github.com/matrix-org/sydent/security/advisories/GHSA-pw4v-gr34-2553

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