QID 982084

QID 982084: Python (pip) Security Update for fastapi (GHSA-8h2j-cgx8-6xv7)

Security update has been released for fastapi to fix the vulnerability.

Note: The preceding description block is extracted directly from the security advisory. Using automation, we have attempted to clean and format it as much as possible without introducing additional issues.

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](https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS) preflights, for being considered [Simple requests](https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#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.

CVSS V3 rated as Critical - 8.1 severity.

CVSS V2 rated as Medium - 5.8 severity.

Solution

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`.Workaround:
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.

Vendor References

GHSA-8h2j-cgx8-6xv7 - github.com/advisories/GHSA-8h2j-cgx8-6xv7

CVEs related to QID 982084

CVE-2021-32677 |

Software Advisories

Advisory ID	Software	Component	Link
GHSA-8h2j-cgx8-6xv7	fastapi		github.com/advisories/GHSA-8h2j-cgx8-6xv7

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