---
id: CVE-2021-29433
aliases:
  - GHSA-pw4v-gr34-2553
  - PYSEC-2021-24
title: Sydent DoS (via resource exhaustion) due to improper input validation
summary: Sydent DoS (via resource exhaustion) due to improper input validation
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L'
vendor: matrix-sydent
product: matrix-sydent
ecosystem: pip
affected:
  - matrix-sydent < 2.3.0
patched:
  - matrix-sydent 2.3.0
published: '2021-04-16'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:49:03.750308427Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-pw4v-gr34-2553'
references:
  - url: >-
      https://github.com/matrix-org/sydent/security/advisories/GHSA-pw4v-gr34-2553
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2021-29433'
  - url: >-
      https://github.com/matrix-org/sydent/commit/3175fd358ebc2c310eab7a3dbf296ce2bd54c1da
  - url: 'https://github.com/matrix-org/sydent'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/matrix-sydent/PYSEC-2021-24.yaml
  - url: 'https://pypi.org/project/matrix-sydent'
tags:
  - osv
  - pip
epss: 0.00927
epssPercentile: 0.58802
ingestedAt: '2026-09-12T03:13:01.718Z'
---

## Overview

### Impact

Missing 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.

### Patches

Fixed by 3175fd3.

### For more information

If you have any questions or comments about this advisory, email us at security@matrix.org.

## Affected packages

- `matrix-sydent < 2.3.0`

## Remediation

Upgrade to a patched release:

- `matrix-sydent 2.3.0`