Path Traversal in Fastify Fastify\/http-Proxy
CVE-2026-85124
@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.
Vulnerability class: Path Traversal (Directory Traversal)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.007 (53.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 54th percentile — 53.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.006 · newest: 0.007 · change: +0.002
Affected products
Weakness classification (CWE)
References
- ce714d77-add3-4f53-aff5-83d477b104bb (Third Party Advisory)
- ce714d77-add3-4f53-aff5-83d477b104bb (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-85124?
- CVE-2026-85124 is a high-severity vulnerability in Fastify Fastify\/http-Proxy, classified under Path Traversal. CVSS score: 7.5/10. Published 2026-09-03.
- How severe is CVE-2026-85124?
- High severity. CVSS v3 base score is 7.5 out of 10.