CVE-2026-25223
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.80%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- EPSS
- 0.80% probability · 55th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-436, CWE-179
- Affected
- fastify/fastify
- Source
- security-advisories@github.com
References
- https://fastify.dev/docs/latest/Reference/Validation-and-SerializationProduct, Technical Description
- https://github.com/fastify/fastify/blob/759e9787b5669abf953068e42a17bffba7521348/lib/content-type-parser.js#L125Product
- https://github.com/fastify/fastify/blob/759e9787b5669abf953068e42a17bffba7521348/lib/validation.js#L272Product
- https://github.com/fastify/fastify/commit/32d7b6add39ddf082d92579a58bea7018c5ac821Patch
- https://github.com/fastify/fastify/security/advisories/GHSA-jx2c-rxcm-jvmqMitigation, Vendor Advisory
- https://hackerone.com/reports/3464114Permissions Required
- 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
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.