# CVE-2026-120214: @fastify/http-proxy vulnerable to prefix escape via percent-encoded backslash dot-segments


- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 2 Nov 2026
- **Updated:** 2 Nov 2026
- **Also known as:** GHSA-hr26-gmr2-pwcv

## What is CVE-2026-120214?

CVE-2026-120214 is a medium-severity vulnerability in @fastify/http-proxy, published on 2 Nov 2026. 

### Official description

@fastify/http-proxy is a Fastify plugin that proxies HTTP requests to an upstream server under a configured prefix. In versions 11.6.0 through 11.6.2, the destination validation normalizes literal backslashes before it percent-decodes the request path, so a path that encodes its backslashes and dot-segments survives the dot-segment check and is only turned into backslash and double-dot sequences after that check has passed. When the upstream resolves on a platform that treats a backslash as a path separator, the forwarded request walks out of the configured proxy prefix and reaches a sibling location on the upstream. An unauthenticated remote attacker can use this to retrieve upstream resources outside the intended prefix, so the impact is confidentiality only, and exploitation depends on the upstream's path handling. The issue is fixed in @fastify/http-proxy 11.6.3, and users should upgrade to 11.6.3 or later. This is a follow-up to the earlier prefix-escape fix, which did not account for the encoded-backslash form.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-120214?


## How do I fix CVE-2026-120214?

No fix has been published for CVE-2026-120214 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-120214 being exploited?

There is no known exploitation of CVE-2026-120214 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-120214 and fix it if it is affected.

What it is: CVE-2026-120214 is a medium-severity vulnerability in @fastify/http-proxy, published on 2 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-120214 in the wild and no public exploit code.

Affected product: @fastify/http-proxy. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-120214/ (Markdown: https://insights.sbomify.com/CVE-2026-120214/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-120214
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-120214
- OSV: https://osv.dev/vulnerability/CVE-2026-120214

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-120214/
Summaries are generated and may contain mistakes; the official description above is the record.