Cross-Site Request Forgery (CSRF) in FastAPI
Impact
FastAPI versions lower than 0.65.2 that used cookies for authentication in path operations that received JSON payloads sent by browsers were vulnerable to a Cross-Site Request Forgery (CSRF) attack.
In versions lower than 0.65.2, FastAPI would try to read the request payload as JSON even if the content-type header sent was not set to application/json or a compatible JSON media type (e.g. application/geo+json).
So, a request with a content type of text/plain containing JSON data would be accepted and the JSON data would be extracted.
But requests with content type text/plain are exempt from CORS preflights, for being considered Simple requests. So, the browser would execute them right away including cookies, and the text content could be a JSON string that would be parsed and accepted by the FastAPI application.
Patches
This is fixed in FastAPI 0.65.2.
The request data is now parsed as JSON only if the content-type header is application/json or another JSON compatible media type like application/geo+json.
Workarounds
It's best to upgrade to the latest FastAPI.
But still, it would be possible to add a middleware or a dependency that checks the content-type header and aborts the request if it is not application/json or another JSON compatible content type.
References
For more information
If you have any questions or comments, write to security@tiangolo.com
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | fastapi | < 0.65.2 | 0.65.2 |
References
- https://github.com/tiangolo/fastapi/commit/fa7e3c996edf2d5482fff8f9d890ac2390dede4d
- https://github.com/tiangolo/fastapi/security/advisories/GHSA-8h2j-cgx8-6xv7
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/MATAWX25TYKNEKLDMKWNLYDB34UWTROA/
- https://nvd.nist.gov/vuln/detail/CVE-2021-32677
- https://github.com/pypa/advisory-database/tree/main/vulns/fastapi/PYSEC-2021-100.yaml
- https://github.com/tiangolo/fastapi
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/MATAWX25TYKNEKLDMKWNLYDB34UWTROA
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N- Weakness (CWE)
CWE-352- Platform
- Python (PyPI)
- Package
fastapi- Disclosed
- 09.06.2021
- Updated
- 11.10.2026 13:19
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2021-100 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-8h2j-cgx8-6xv7 - CC BY 4.0
Vulnerability history: fastapi
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 2
- First → latest
- 06.2021 02.2024
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 2
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 0
- 2024: 1
- 2025: 0
- 2026: 0
-
Cross-Site Request Forgery (CSRF) in FastAPI this entry
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