Vulnerability · Published Jul 7, 2025 · Assigned by GitHub_M
CVE-2025-53539ReDoS in fastapi-guard's penetration attempts detector
Medium 6.9
In plain English
A medium-severity regular-expression denial of service in fastapi-guard from rennf93. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 42% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| PyPI | fastapi-guard | 3.0.1 | GHSA-j47q-rc62-w448 |
| PyPI | fastapi-guard | 3.0.1 | PYSEC-2026-1359 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| rennf93 | fastapi-guard | < 3.0.1 |
Weakness: CWE-1333 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N