What’s Vulnerable › Vulnerabilities

CVE-2026-25223: Fastify's Content-Type header tab character allows body validation bypass

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-02-03 · updated 2026-07-15
• Weakness: CWE-436

Description

Fastify is a fast and low overhead web framework, for Node.js. Prior to version 5.7.2, a validation bypass vulnerability exists in Fastify where request body validation schemas specified by Content-Type can be completely circumvented. By appending a tab character (\t) followed by arbitrary content to the Content-Type header, attackers can bypass body validation while the server still processes the body as the original content type. This issue has been patched in version 5.7.2.

Affected products

• fastify: before 5.7.2 — fixed in 5.7.2

How to fix

Upgrade to a fixed version: fastify 5.7.2. Check the vendor advisory for mitigations.

References

• https://fastify.dev/docs/latest/Reference/Validation-and-Serialization
• https://github.com/fastify/fastify/blob/759e9787b5669abf953068e42a17bffba7521348/lib/content-type-parser.js#L125
• https://github.com/fastify/fastify/blob/759e9787b5669abf953068e42a17bffba7521348/lib/validation.js#L272
• https://github.com/fastify/fastify/commit/32d7b6add39ddf082d92579a58bea7018c5ac821
• https://github.com/fastify/fastify/security/advisories/GHSA-jx2c-rxcm-jvmq
• https://hackerone.com/reports/3464114
• https://access.redhat.com/errata/RHSA-2026:10184
• https://access.redhat.com/errata/RHSA-2026:5807
• https://access.redhat.com/errata/RHSA-2026:6192
• https://access.redhat.com/security/cve/CVE-2026-25223
• https://bugzilla.redhat.com/show_bug.cgi?id=2436560
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-25223.json

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