Headline
GHSA-95c6-p277-p87g: FastAPI Api Key has a timing side-channel in verify_key that allows statistical key validity detection
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
- GitHub Advisory Database
- GitHub Reviewed
- CVE-2026-23996
FastAPI Api Key has a timing side-channel in verify_key that allows statistical key validity detection
Package
pip fastapi-api-key (pip)
Affected versions
< 1.1.0
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
References
- GHSA-95c6-p277-p87g
- Athroniaeth/fastapi-api-key@310b2c5
- https://github.com/Athroniaeth/fastapi-api-key/releases/tag/1.1.0
Published to the GitHub Advisory Database
Jan 21, 2026
Last updated
Jan 21, 2026