CVE-2026-85124
@fastify/http-proxy vulnerable to prefix escape via backslash dot-segments
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.
INFO
Published Date :
Sept. 3, 2026, 1:06 p.m.
Last Modified :
Sept. 9, 2026, 7:25 p.m.
Remotely Exploit :
No
Source :
ce714d77-add3-4f53-aff5-83d477b104bb
Affected Products
The following products are affected by CVE-2026-85124
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | ce714d77-add3-4f53-aff5-83d477b104bb | ||||
| CVSS 3.1 | HIGH | MITRE-CVE |
Solution
- Upgrade @fastify/http-proxy to 11.6.2 or later.
- Validate proxied HTTP request paths.
- Ensure upstream paths are not exposed.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-85124.
| URL | Resource |
|---|---|
| https://cna.openjsf.org/security-advisories.html | Third Party Advisory |
| https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-qv33-689p-2xq5 | Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-85124 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-85124
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-85124 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-85124 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Sep. 09, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:fastify:fastify/http-proxy:*:*:*:*:*:node.js:*:* versions up to (excluding) 11.6.2 Added Reference Type openjs: https://cna.openjsf.org/security-advisories.html Types: Third Party Advisory Added Reference Type openjs: https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-qv33-689p-2xq5 Types: Vendor Advisory -
New CVE Received by ce714d77-add3-4f53-aff5-83d477b104bb
Sep. 03, 2026
Action Type Old Value New Value Added 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Added CWE CWE-22 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/85xxx/CVE-2026-85124.json">CVE-2026-85124</a> Added Reference https://cna.openjsf.org/security-advisories.html Added Reference https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-qv33-689p-2xq5 -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Sep. 03, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-85124', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-09-03T12:31:02.813629Z'}