How severe is CVE-2025-53539?

CVE-2025-53539 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2025-53539 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (34th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-53539?

CVE-2025-53539 affects Fastapi-guard Fastapi Guard. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-53539?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2025-53539 have an EU (EUVD) identifier?

Yes. CVE-2025-53539 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-20307.

When was CVE-2025-53539 published?

CVE-2025-53539 was published on 2025-07-07 and last updated on 2026-06-17.

CVE-2025-53539

CVE-2025-53539 is a high-severity vulnerability in Fastapi-guard Fastapi Guard with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-1333.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v4: 6.9
EPSS exploit prediction: 0% (34th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-20307
Weakness: CWE-1333
Affected product: Fastapi-guard Fastapi Guard
Published: 2025-07-07
Last modified: 2026-06-17

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.

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.
How severe is CVE-2025-53539?: CVE-2025-53539 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2025-53539 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (34th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-53539?: CVE-2025-53539 affects Fastapi-guard Fastapi Guard. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-53539?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2025-53539 have an EU (EUVD) identifier?: Yes. CVE-2025-53539 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-20307.
When was CVE-2025-53539 published?: CVE-2025-53539 was published on 2025-07-07 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:fastapi-guard:fastapi_guard:*:*:*:*:*:*:*:*

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