CVE-2026-23996

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

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

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.

CVE-2026-23996 has a CVSS score of 3.7 (Low). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.1.0); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

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.

1. What is CVE-2026-23996? CVE-2026-23996 is a low-severity security vulnerability in fastapi-api-key (pip), affecting versions < 1.1.0. It is fixed in 1.1.0.
2. How severe is CVE-2026-23996? CVE-2026-23996 has a CVSS score of 3.7 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of fastapi-api-key are affected by CVE-2026-23996? fastapi-api-key (pip) versions < 1.1.0 is affected.
4. Is there a fix for CVE-2026-23996? Yes. CVE-2026-23996 is fixed in 1.1.0. Upgrade to this version or later.
5. Is CVE-2026-23996 exploitable, and should I be worried? Whether CVE-2026-23996 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-23996 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-23996? Upgrade fastapi-api-key to 1.1.0 or later.