FastAPI Api Key has a timing side-channel in verify_key that allows statistical key validity detection

Exploitation

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

CVSS

3.7 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2026-23996: 0.29% estimated exploitation activity in the next 30 days; percentile 21.79 (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.

Impact Timing side-channel vulnerability in verifykey(). The method applied a random delay only on verification failures, allowing an attacker to statistically distinguish valid from invalid API keys by measuring response latencies. With enough repeated requests, an adversary could infer whether a keyid corresponds to a valid key, potentially accelerating brute-force or enumeration attacks. Affected: all users relying on verifykey() for API key authentication prior to the fix. Patches Yes. Users should upgrade to version 1.1.0 (or the version containing this fix). The patch applies a uniform random delay (mindelay to maxdelay) to all responses regardless of outcome, eliminating the timing correlation. Workarounds - Add an application-level fixed delay or random jitter to all authentication responses (success and failure) before the fix is applied. - Use rate limiting to reduce the feasibility of statistical timing attacks. References - CWE-208: Observable Timing Discrepancy - Commit:…

Published by the source

21 Jan 2026, 22:27 UTC

Last modified by the source

7 Jul 2026, 17:57 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-95c6-p277-p87g

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-95c6-p277-p87g

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# Patch Next advisory brief: CVE-2026-23996

Advisory: FastAPI Api Key has a timing side-channel in verify_key that allows statistical key validity detection
IDs: CVE-2026-23996, GHSA-95c6-p277-p87g
Record: https://patchnext.com/advisories/cve-2026-23996 (revision 2, 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: Low (CVSS 3.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: fastapi-api-key 1.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI fastapi-api-key: affected < 1.1.0; fixed in 1.1.0

## Suggested inspection (read-only)
- `python -m pip show fastapi-api-key`: 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-api-key.
- 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-95c6-p277-p87g (OSV record GHSA-95c6-p277-p87g lists affected ranges: PyPI fastapi-api-key >=0 <1.1.0 (fixed))
- Verified: https://github.com/advisories/GHSA-95c6-p277-p87g (GitHub-reviewed advisory GHSA-95c6-p277-p87g lists affected ranges: PyPI fastapi-api-key >=0 <1.1.0)

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