CVE-2026-23996

Summary

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.

Affected Software

VendorProductVersion RangeStatus
Athroniaethfastapi-api-key< 1.1.0affected

Weaknesses

  • CWE-208: CWE-208: Observable Timing Discrepancy

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

References