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TI-2025-33483 Aliases CVE-2025-53539GHSA-j47q-rc62-w448

ReDoS in fastapi-guard's penetration attempts detector

Priority MEDIUM 64CWE-1333Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · Low
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub. Impact type from CWE-1333.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00481 41st percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed fastapi-guard (rennf93): 3.0.1fastapi-guard (PyPI): 3.0.1

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
rennf93fastapi-guardbefore 3.0.13.0.1Patch availableCNA
—fastapi-guard (PyPI)before 3.0.13.0.1Patch availableGHSA-j47q-rc62-w448
  • fastapi-guard Vendorrennf93 Affected before 3.0.1 Fixed in 3.0.1 Patch available CNA
  • fastapi-guard (PyPI) Vendor— Affected before 3.0.1 Fixed in 3.0.1 Patch available GHSA-j47q-rc62-w448

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:fastapi-guard:fastapi_guard:*:*:*:*:*:*:*:*before 3.0.1Vulnerablerennf93
  • cpe:2.3:a:fastapi-guard:fastapi_guard:*:*:*:*:*:*:*:* Versions before 3.0.1 Vulnerable ·rennf93

Remediation

  • Fix · CNA fastapi-guard (rennf93) Fixed in 3.0.1
  • Fix · GHSA-j47q-rc62-w448 fastapi-guard (PyPI) Fixed in 3.0.1 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2025-53539
  2. 2026-10-03 Alias added: GHSA-j47q-rc62-w448

References

Exploit 1

Patch 1

Advisory 1

Other 1

  • TI-2025-34178 fastapi-guard patch contains bypassable RegEx CVSS 4.0HIGH 7.8
  • TI-2025-29447 FastAPI Guard Remote Header Injection via X-Forwarded-For Manipulation CVSS 3.1HIGH 7.5

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences