# CVE-2025-53539: PYSEC-2026-1359 - fastapi-guard is vulnerable to ReDoS through inefficient regex

Source: https://junglewise.ai/threats/cve-2025-53539-fastapi-guard-is-vulnerable-to-redos-through-inefficient-regex  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-07  
License: CC BY 4.0 with a link back

CVE-2025-53539 · Severity: medium · CVSS 4 · Published 2026-07-07

fastapi-guard is vulnerable to ReDoS through inefficient regex

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

## Quick answers

**Is CVE-2025-53539 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-53539 being exploited in the wild.

**How severe is CVE-2025-53539?** Medium severity, with a CVSS score of 4, published 7 July 2026.

**Which products and versions are affected?** fastapi-guard (PyPI) ECOSYSTEM:introduced=0,fixed=3.0.1.

**Is there a fix for CVE-2025-53539?** Yes. fastapi-guard (PyPI): upgrade to 3.0.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2025-53539?** Check whether you run fastapi-guard (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

- fastapi-guard (PyPI): upgrade to 3.0.1 or later

  ```sh
  pip install "fastapi-guard>=3.0.1"
  ```


## Affected products

- fastapi-guard (PyPI) ECOSYSTEM:introduced=0,fixed=3.0.1

## Identifiers

- CVE-2025-53539
- GHSA-j47q-rc62-w448
- PYSEC-2026-1359

## Related threats

- [PYSEC-2026-1360 - FastAPI Guard has a regex bypass](https://junglewise.ai/threats/cve-2025-54365-fastapi-guard-has-a-regex-bypass)
- [PYSEC-2025-242 - FastAPI Guard is a security library for FastAPI that provides middleware to control IPs, log…](https://junglewise.ai/threats/cve-2025-46814-pysec-2025-242-fastapi-guard-is-a-security-library-for-fastapi)