CVE-2025-53539 json
ReDoS in fastapi-guard's penetration attempts detector
published 2025-07-07 16 mo ago modified 2026-07-07 4 mo ago also EUVD-2025-20307 , GHSA-j47q-rc62-w448 , PYSEC-2026-1359
- cvss
- 7.5
- version 3.1, NVD
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.5%
- EPSS 0.5% chance of exploitation in 30 days, percentile 41%
- public exploits
- 0
- none known
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.
Patch / fix
- pypi fastapi-guard 3.0.1
- fastapi-guard fastapi_guard 3.0.1
CISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- no
- Technical impact
- partial
- Assessed
- 16 mo ago
Exploit prediction
0.48% chance of exploitation in the next 30 days, higher than 41% of all scored CVEs (FIRST EPSS, 2026-11-08).
Exploits and checks
- github.com https://github.com/rennf93/fastapi-guard/security/advisories/GHSA-j47q-rc62-w448 referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 4.0 | 6.9 | 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 |
| CNA | 4.0 | 6.9 | 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X |
| NVD | 3.1 | 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| pypi | fastapi-guard | <3.0.1 |
3.0.1 |
Affected products
- rennf93 fastapi-guard
Classification
- Weakness
-
- CWE-1333 Inefficient Regular Expression Complexity
References
-
github.com
/rennf93/fastapi-guard/commit/d9d50e8130b7b434cdc1b001b8cfd03a06729f7f
web, patch
-
github.com
/rennf93/fastapi-guard/security/advisories/GHSA-j47q-rc62-w448
web, exploit, vendor-advisory
-
nvd.nist.gov
/vuln/detail/CVE-2025-53539
advisory
-
github.com
/rennf93/fastapi-guard
package
-
pypi.org
/project/fastapi-guard
package
-
github.com
/advisories/GHSA-j47q-rc62-w448
advisory
Sources
- CVE List CVE-2025-53539
- GitHub Advisory GHSA-j47q-rc62-w448
- NVD CVE-2025-53539
- OSV PYSEC-2026-1359
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.