CVE-2026-23996 is a low-severity (CVSS 3.7) CWE-208 vulnerability in fastapi-api-key. A fix is available for fastapi-api-key — see the affected versions and patch details below.
FastAPI Api Key has a timing side-channel in verify_key that allows statistical key validity detection
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-23996.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
fastapi-api-keyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
Timing side-channel vulnerability in verify_key(). 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 key_id corresponds to a valid key, potentially accelerating brute-force or enumeration attacks.
Affected: all users relying on verify_key() 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 (min_delay to max_delay) 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: 87b27640f77c5ef86c46311b6b5a7e2887e35b77
- OWASP: https://owasp.org/www-community/attacks/Timing_attack
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | fastapi-api-key | all versions | 1.1.0pip install --upgrade 'fastapi-api-key==1.1.0' |
Affected Products
fastapi api keyathroniaethDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastapi-api-key, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update fastapi-api-key to 1.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-23996 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-23996 in your dependencies?
Find it across PyPI, including transitive dependencies.