# CVE-2021-29431: SSRF in Sydent due to missing validation of hostnames

Source: https://junglewise.ai/threats/cve-2021-29431-ssrf-in-sydent-due-to-missing-validation-of-hostnames  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2021-04-15  
License: CC BY 4.0 with a link back

CVE-2021-29431 · Severity: low · CVSS 3.1 · Published 2021-04-15

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.

Technologies: [matrix-sydent (PyPI)](https://junglewise.ai/threats/technologies/matrix-sydent). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2021-29431 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2021-29431 being exploited in the wild.

**How severe is CVE-2021-29431?** Low severity, with a CVSS score of 3.1, published 15 April 2021.

**Which products and versions are affected?** matrix-sydent (PyPI) ECOSYSTEM:introduced=0,fixed=2.3.0, GIT:introduced=0,fixed=3d531ed50d2fd41ac387f36d44d3fb2c62dd22d3,fixed=0f00412017f25619bc36c264b29ea96808bf310a,fixed=9e573348d81df8191bbe8c266c01999c9d57cd5f,fixed=8936925f561b0c352c2fa922d5097d7245aad00a|ECOSYSTEM:introduced=0,fixed=2.3.0.

**Is there a fix for CVE-2021-29431?** Yes. matrix-sydent (PyPI): upgrade to 2.3.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2021-29431?** Check whether you run matrix-sydent (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- matrix-sydent (PyPI): upgrade to 2.3.0 or later

  ```sh
  pip install "matrix-sydent>=2.3.0"
  ```


## Affected products

- matrix-sydent (PyPI) ECOSYSTEM:introduced=0,fixed=2.3.0, GIT:introduced=0,fixed=3d531ed50d2fd41ac387f36d44d3fb2c62dd22d3,fixed=0f00412017f25619bc36c264b29ea96808bf310a,fixed=9e573348d81df8191bbe8c266c01999c9d57cd5f,fixed=8936925f561b0c352c2fa922d5097d7245aad00a|ECOSYSTEM:introduced=0,fixed=2.3.0

## Identifiers

- CVE-2021-29431
- GHSA-9jhm-8m8c-c3f4
- PYSEC-2021-22

## Related threats

- [PYSEC-2026-2620 - matrix-sydent and matrix-synapse Use Cryptographically Weak PRNG](https://junglewise.ai/threats/cve-2019-11842-matrix-sydent-and-matrix-synapse-use-cryptographically-weak-prng)
- [PYSEC-2026-843 - Matrix Sydent mishandles emails](https://junglewise.ai/threats/cve-2019-11340-matrix-sydent-mishandles-emails)
- [Sydent does not verify email server certificates](https://junglewise.ai/threats/cve-2023-38686-sydent-does-not-verify-email-server-certificates)
- [Malicious users could abuse Sydent to control the content of invitation emails](https://junglewise.ai/threats/cve-2021-29432-malicious-users-could-abuse-sydent-to-control-the-content-of)
- [Sydent vulnerable to denial of service attack via memory exhaustion](https://junglewise.ai/threats/cve-2021-29430-sydent-vulnerable-to-denial-of-service-attack-via-memory)