CVE-2026-23996
FastAPI Api Key has a timing side-channel in verify_key that allows statistical key validity detection
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
How to fix CVE-2026-23996
To remediate CVE-2026-23996, upgrade the affected package to a fixed version below.
- —upgrade to 1.1.0 or later
Is CVE-2026-23996 being exploited?
Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- from 0, < 1.1.0