Interpretation Conflict Affecting fastify package, versions <5.7.2
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
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-FASTIFY-15182642
- published3 Feb 2026
- disclosed2 Feb 2026
- creditUnknown
Introduced: 2 Feb 2026
NewCVE-2026-25223 (opens in a new tab)How to fix?
Upgrade fastify to version 5.7.2 or higher.
Overview
fastify is an overhead web framework, for Node.js.
Affected versions of this package are vulnerable to Interpretation Conflict via the Content-Type header processing. An attacker can bypass body validation by appending a tab character (\t) and arbitrary content to the Content-Type header, causing the server to treat the body as the intended type without enforcing validation rules.
Note: This vulnerability affects all Fastify users who rely on Content-Type-based body validation schemas to enforce data integrity or security constraints.
Workaround
This vulnerability can be mitigated by implementing a custom onRequest hook to reject requests containing tab characters in the Content-Type header.