@fastify/reply-from JSON Content-Type parsing confusion

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2023-51701: 0.48% estimated exploitation activity in the next 30 days; percentile 41.37 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact The main repo of fastify use fast-content-type-parse to parse request Content-Type, which will trim after split. The fastify-reply-from have not use this repo to unify the parse of Content-Type, which won't trim. As a result, a reverse proxy server built with @fastify/reply-from could misinterpret the incoming body by passing an header ContentType: application/json ; charset=utf-8. This can lead to bypass of security checks. Patches @fastify/reply-from v9.6.0 include the fix. Workarounds There are no known workarounds. References Hackerone Report: https://hackerone.com/reports/2295770.

Published by the source

8 Jan 2024, 15:22 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:30 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-v2v2-hph8-q5xp

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-v2v2-hph8-q5xp

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# Patch Next advisory brief: CVE-2023-51701

Advisory: @fastify/reply-from JSON Content-Type parsing confusion
IDs: CVE-2023-51701, GHSA-v2v2-hph8-q5xp
Record: https://patchnext.com/advisories/cve-2023-51701 (revision 2, source checked 26 Oct 2026, 12:30 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @fastify/reply-from 9.6.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @fastify/reply-from: affected < 9.6.0; fixed in 9.6.0

## Suggested inspection (read-only)
- `npm ls @fastify/reply-from --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @fastify/reply-from.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-v2v2-hph8-q5xp (OSV record GHSA-v2v2-hph8-q5xp lists affected ranges: npm @fastify/reply-from >=0 <9.6.0 (fixed))
- Verified: https://github.com/advisories/GHSA-v2v2-hph8-q5xp (GitHub-reviewed advisory GHSA-v2v2-hph8-q5xp lists affected ranges: npm @fastify/reply-from >=0 <9.6.0)

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