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

> Attackers can bypass request body validation in Fastify by appending a tab character to the Content-Type header, allowing unvalidated data processing.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 3 Feb 2026
- **Updated:** 16 Sep 2026
- **Also known as:** GHSA-jx2c-rxcm-jvmq, MINI-76p2-695q-hg3p

## What is CVE-2026-25223?

CVE-2026-25223 is a high-severity vulnerability in fastify, published on 3 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-179 (Incorrect Behavior Order: Early Validation), CWE-436 (Interpretation Conflict)

## Which versions are affected by CVE-2026-25223?

2 open source packages ship an affected version, including fastify. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `fastify` | npm | All versions | 5.7.2 |
| `fastify` | npm | All versions | 5.7.2 |

Products: Fastify Fastify.

## How do I fix CVE-2026-25223?

Upgrade fastify to 5.7.2 or later.

## Is CVE-2026-25223 being exploited?

There is no known exploitation of CVE-2026-25223 in the wild and no public exploit code.

## Other vulnerabilities in fastify

- [CVE-2026-84504](https://insights.sbomify.com/CVE-2026-84504/): fastify vulnerable to request body replacement via an async validation result collision (high 8.1)
- [CVE-2026-76169](https://insights.sbomify.com/CVE-2026-76169/): fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers (high 7.5)
- [CVE-2026-84428](https://insights.sbomify.com/CVE-2026-84428/): fastify vulnerable to header validation bypass via incomplete schema case normalization (high 7.5)
- [CVE-2026-84469](https://insights.sbomify.com/CVE-2026-84469/): fastify vulnerable to request validation bypass via skipped boolean false schemas (high 7.5)
- [CVE-2026-33806](https://insights.sbomify.com/CVE-2026-33806/): fastify vulnerable to Body Schema Validation Bypass via Leading Space in Content-Type Header (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-25223 and fix it if it is affected.

What it is: CVE-2026-25223 is a high-severity vulnerability in fastify, published on 3 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-25223 in the wild and no public exploit code.

Affected packages and fixed versions:
- fastify (npm): affected all versions; fixed in 5.7.2
- fastify (npm): affected all versions; fixed in 5.7.2

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-25223/ (Markdown: https://insights.sbomify.com/CVE-2026-25223/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-25223
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-25223
- OSV: https://osv.dev/vulnerability/CVE-2026-25223

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-25223/
Summaries are generated and may contain mistakes; the official description above is the record.