FastAPI SSP is vulnerable to Cross-site Request Forgery (CSRF) through improper OAuth parameter validation

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N/E:P · score source

EPSS

• CVE-2025-14546: 0.36% estimated exploitation activity in the next 30 days; percentile 29.68 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Versions of the package fastapi-sso before 0.19.0 are vulnerable to Cross-site Request Forgery (CSRF) due to the improper validation of the OAuth state parameter during the authentication callback. While the getloginurl method allows for state generation, it does not persist the state or bind it to the user's session. Consequently, the verifyandprocess method accepts the state received in the query parameters without verifying it against a trusted local value. This allows a remote attacker to trick a victim into visiting a malicious callback URL, which can result in the attacker's account being linked to the victim's internal account.

Published by the source

19 Dec 2025, 06:30 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-hp6r-r9vc-q8wx

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-hp6r-r9vc-q8wx

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# Patch Next advisory brief: CVE-2025-14546

Advisory: FastAPI SSP is vulnerable to Cross-site Request Forgery (CSRF) through improper OAuth parameter validation
IDs: CVE-2025-14546, GHSA-hp6r-r9vc-q8wx
Record: https://patchnext.com/advisories/cve-2025-14546 (revision 3, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: fastapi-sso 0.19.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI fastapi-sso: affected < 0.19.0; fixed in 0.19.0

## Suggested inspection (read-only)
- `python -m pip show fastapi-sso`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on fastapi-sso.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-hp6r-r9vc-q8wx (OSV record GHSA-hp6r-r9vc-q8wx lists affected ranges: PyPI fastapi-sso >=0 <0.19.0 (fixed))
- Verified: https://github.com/advisories/GHSA-hp6r-r9vc-q8wx (GitHub-reviewed advisory GHSA-hp6r-r9vc-q8wx lists affected ranges: PyPI fastapi-sso >=0 <0.19.0)

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