---
id: CVE-2021-29431
aliases:
  - GHSA-9jhm-8m8c-c3f4
  - PYSEC-2021-22
title: SSRF in Sydent due to missing validation of hostnames
summary: SSRF in Sydent due to missing validation of hostnames
severity: high
cvss: 7.7
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N'
vendor: matrix-sydent
product: matrix-sydent
ecosystem: pip
affected:
  - matrix-sydent < 2.3.0
patched:
  - matrix-sydent 2.3.0
published: '2021-04-19'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:49:03.074179988Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-9jhm-8m8c-c3f4'
references:
  - url: >-
      https://github.com/matrix-org/sydent/security/advisories/GHSA-9jhm-8m8c-c3f4
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2021-29431'
  - url: >-
      https://github.com/matrix-org/sydent/commit/0f00412017f25619bc36c264b29ea96808bf310a
  - url: >-
      https://github.com/matrix-org/sydent/commit/3d531ed50d2fd41ac387f36d44d3fb2c62dd22d3
  - url: >-
      https://github.com/matrix-org/sydent/commit/8936925f561b0c352c2fa922d5097d7245aad00a
  - url: >-
      https://github.com/matrix-org/sydent/commit/9e573348d81df8191bbe8c266c01999c9d57cd5f
  - url: 'https://github.com/matrix-org/sydent'
  - url: 'https://github.com/matrix-org/sydent/releases/tag/v2.3.0'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/matrix-sydent/PYSEC-2021-22.yaml
  - url: 'https://pypi.org/project/matrix-sydent'
tags:
  - osv
  - pip
epss: 0.01194
epssPercentile: 0.66669
ingestedAt: '2026-09-12T03:13:01.684Z'
---

## Overview

### Impact

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.

### Patches

Fixed in 9e57334, 8936925, 3d531ed, 0f00412

### Workarounds

A potential workaround would be to use a firewall to ensure that Sydent cannot reach internal HTTP resources.

### 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`