Race Condition Affecting @fastify/session package, versions <11.1.6
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JS-FASTIFYSESSION-21755406
- published27 Oct 2026
- disclosed27 Oct 2026
- creditYounghun Ko, BlueN0r
Introduced: 27 Oct 2026
NewCVE-2026-117499 (opens in a new tab)How to fix?
Upgrade @fastify/session to version 11.1.6 or higher.
Overview
@fastify/session is an a session plugin for fastify
Affected versions of this package are vulnerable to Race Condition via Session.decodeSessionId and the session restoration logic in index.js, where a stale or superseded session cookie can be used to restore a session that should no longer be valid. An attacker who holds an old session identifier can replay it to regain access to a session that has been regenerated, because the generation check (getSessionGeneration) was absent, allowing the store lookup to succeed and the old session to be restored without verifying that the cookie's embedded generation matches the stored session's current generation.