CVE-2026-23996

CVE-2026-23996 · FastAPI Api Key has a timing side-channel in verify_key that allows statistical key validity detection

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FastAPI Api Key provides a backend-agnostic library that provides an API key system. Version 1.1.0 has a 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. All users relying on verify_key() for API key authentication prior to the fix are affected. Users should upgrade to version 1.1.0 to receive a patch. The patch applies a uniform random delay (min_delay to max_delay) to all responses regardless of outcome, eliminating the timing correlation. Some workarounds are available. Add an application-level fixed delay or random jitter to all authentication responses (success and failure) before the fix is applied and/or use rate limiting to reduce the feasibility of statistical timing attacks.

CVSS 3.7 · Low · EPSS 0.3% · Fix available

Published

2026-01-21T22:29:24.107Z

Updated

2026-01-22T16:49:16.733Z

Stack: python

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