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CVE-2026-85124

7.5 · HIGH

@fastify/http-proxy versions before 11.6.2 do not validate proxied HTTP request paths for backslash based dot-segments before forwarding them to the configured upstream.

Published Sep 3, 2026fastifyCWE-22EPSS 0.74%

Overview

CVE-2026-85124 is a high-severity vulnerability affecting fastify fastify\/http-proxy. It was published on September 3, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

@fastify/http-proxy versions before 11.6.2 do not validate proxied HTTP request paths for backslash based dot-segments before forwarding them to the configured upstream. The plain HTTP request handler skips the destination validation that the WebSocket path performs, and the underlying reply-from library only rejects forward-slash traversal, so a request containing backslash dot-segments can escape the boundary set by the prefix and rewritePrefix options. An unauthenticated network attacker can use this to reach upstream paths that were meant to stay hidden behind the proxy, resulting in disclosure of internal endpoints. This is a path traversal issue (CWE-22). Users should upgrade to @fastify/http-proxy 11.6.2 or later.

Remediation

Check the references section for vendor advisories and patches from fastify. Update fastify\/http-proxy to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected products

VendorProductVersionsStatus
fastifyfastify\/http-proxy>= 0, < 11.6.2Affected

References

Refcna.openjsf.org/security-advisories.htmlGitHubgithub.com/fastify/fastify-http-proxy/security/advisories/GHSA-qv33-689p-2xq5

How CyberStrike helps

Frequently asked questions

What is CVE-2026-85124?

CVE-2026-85124 is a high-severity vulnerability affecting fastify fastify\/http-proxy. It was published on September 3, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-85124?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-85124?

Check the references section for vendor advisories and patches from fastify. Update fastify\/http-proxy to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-85124?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-85124 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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