CVE-2025-53539: fastapi guard — Exploit & Fix

Description

FastAPI Guard is a security library for FastAPI that provides middleware to control IPs, log requests, and detect penetration attempts. fastapi-guard's penetration attempts detection uses regex to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs. This vulnerability is fixed in 3.0.1.

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CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-1333 CWE-1333

Affected Products

Vendor	Product	Versions
fastapi-guard	fastapi_guard	< 3.0.1

References

Advisories & Patches

https://github.com/rennf93/fastapi-guard/commit/d9d50e8130b7b434cdc1b001b8cfd03a06729f7f https://github.com/rennf93/fastapi-guard/security/advisories/GHSA-j47q-rc62-w448

Exploits

https://github.com/rennf93/fastapi-guard/security/advisories/GHSA-j47q-rc62-w448

Frequently Asked Questions

What is CVE-2025-53539? +

FastAPI Guard is a security library for FastAPI that provides middleware to control IPs, log requests, and detect penetration attempts. fastapi-guard's penetration attempts detection uses regex to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs. This vulnerability is fixed in 3.0.1. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2025-53539? +

CVE-2025-53539 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2025-53539? +

CVE-2025-53539 affects products from fastapi-guard, specifically: fastapi_guard. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-53539? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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