# CVE-2026-120214: @fastify/http-proxy path traversal via percent-encoded backslash

Source: https://junglewise.ai/threats/cve-2026-120214-fastify-http-proxy-is-a-fastify-plugin-that-proxies-http  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-02. Updated: 2026-11-02  
License: CC BY 4.0 with a link back

CVE-2026-120214 · Severity: medium · CVSS 5.9 · Published 2026-11-02

@fastify/http-proxy is a Fastify plugin that forwards HTTP requests to an upstream server with path isolation. Versions 11.6.0–11.6.2 fail to properly validate percent-encoded backslashes in request paths, allowing attackers to escape the configured proxy prefix and access unauthorized upstream resources. An unauthenticated remote attacker can retrieve sensitive files or data from the upstream server outside the intended restricted directory.

Technologies: [Fastify @Fastify/Http-Proxy](https://junglewise.ai/threats/technologies/http-proxy). Vendors: [Fastify](https://junglewise.ai/threats/vendors/fastify).

## Quick answers

**Is CVE-2026-120214 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-120214 being exploited in the wild.

**How severe is CVE-2026-120214?** Medium severity, with a CVSS score of 5.9, published 2 November 2026.

**Which products and versions are affected?** Fastify @Fastify/Http-Proxy 11.6.0 through 11.6.2.

**Is there a fix for CVE-2026-120214?** Yes: fixed in @fastify/http-proxy 11.6.3. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-120214 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-120214?** Check whether you run Fastify @Fastify/Http-Proxy at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in @fastify/http-proxy 11.6.3

## Technical details

The vulnerability is a path traversal flaw (CWE-22) where destination validation normalizes literal backslashes before percent-decoding, but does not account for backslashes that appear only after decoding. Requests with percent-encoded backslash dot-segments (%5C..%5C) bypass validateDestination() checks and are forwarded to the upstream intact. On platforms (such as Windows) that treat backslashes as path separators after decoding, the upstream resolves the path outside the rewritePrefix boundary, exposing sibling resources. Attack requires a network-accessible proxy instance and an upstream server that decodes backslashes as path separators.

## Affected products

- Fastify @fastify/http-proxy 11.6.0 through 11.6.2

## Timeline

- 2026-11-02: disclosed

## References

- [https://cna.openjsf.org/security-advisories.html](https://cna.openjsf.org/security-advisories.html)
- [https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-hr26-gmr2-pwcv](https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-hr26-gmr2-pwcv)