GHSA-247c-9743-5963

Описание

Summary

A validation bypass vulnerability exists in Fastify v5.x where request body validation schemas specified via schema.body.content can be completely circumvented by prepending a single space character (\x20) to the Content-Type header. The body is still parsed correctly as JSON (or any other content type), but schema validation is entirely skipped. This is a regression introduced by commit f3d2bcb (fix for CVE-2025-32442).

Details

The vulnerability is a parser-validator differential between two independent code paths that process the raw Content-Type header differently. Parser path (lib/content-type.js, line ~67) applies trimStart() before processing:

Validator path (lib/validation.js, line 272) splits on /[ ;]/ before trimming:

The ContentType class applies trimStart() before processing, so the parser correctly identifies application/json and parses the body. However, getEssenceMediaType splits on /[ ;]/ before trimming, so the leading space becomes a split point, producing an empty string. The validator looks up a schema for content-type "", finds nothing, and skips validation entirely. Regression source: Commit f3d2bcb (April 18, 2025) changed the split delimiter from ';' to /[ ;]/ to fix CVE-2025-32442. The old code (header.split(';', 1)[0].trim()) was not vulnerable to this vector because .trim() would correctly handle the leading space. The new regex-based split introduced the regression.

PoC

Output:

Impact

Any Fastify application that relies on schema.body.content (per-content-type body validation) to enforce data integrity or security constraints is affected. An attacker can bypass all body validation by adding a single space before the Content-Type value. The attack requires no authentication and has zero complexity — it is a single-character modification to an HTTP header. This vulnerability is distinct from all previously patched content-type bypasses:

Recommended fix — add trimStart() before the split in getEssenceMediaType: