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CVE-2021-32677

Cross-Site Request Forgery (CSRF) in fastapi (CVE-2021-32677)

Summary

Vulnerability in fastapi (CVE-2021-32677). Data can be tampered with by attackers. Mitigation: upgrade to 0.65.2 or later.

Original description

The description as published by the source.

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

  • [CORS on Mozilla web…

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2021-32677 has been found in fastapi.
Data can be tampered with by attackers.
What to do: upgrade fastapi to 0.65.2 or later.
If unsure, ask your IT team or search "fastapi CVE-2021-32677" on the vendor's site.

CVE-2021-32677 (fastapi) — CWE-352
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 0.65.2 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

CSRF (CWE-352) exists in fastapi.

📍 Affected scope

Check the vendor advisory for the affected versions of fastapi.

🔥 Severity

Severity: ?. Data can be tampered with by attackers.

🔧 How to fix

Update to 0.65.2.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'fastapi' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'fastapi' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で fastapi を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade fastapi to 0.65.2

    ステージング環境で 0.65.2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

PyPI fastapi
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.65.2"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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