CVE-2026-16117Public exploitNetwork attack vector

Unauthenticated path restriction bypass via encoded prefixes

Published Jul 18, 2026 · Updated Jul 18, 2026

Improper input validation in Fastify @fastify/http-proxy 11.5.0 and earlier allows remote attackers to bypass upstream path restrictions. The prefix-rewrite step applies literal String.replace against the decoded route prefix while request.url retains attacker-supplied percent encoding, so the replacement does not match. Exposure requires a deployment that uses rewritePrefix as a boundary; crafted requests then reach hidden upstream paths, including internal or administrative endpoints.

CVSS severity10.0
Critical
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Fastify @fastify/http-proxy 11.5.0 and earlier allows remote attackers to bypass upstream path restrictions. The prefix-rewrite step applies literal String.replace against the decoded route prefix while request.url retains attacker-supplied percent encoding, so the replacement does not match. Exposure requires a deployment that uses rewritePrefix as a boundary; crafted requests then reach hidden upstream paths, including internal or administrative endpoints.

The record

CVE
CVE-2026-16117
Published
Jul 18, 2026
Updated
Jul 18, 2026
Vendor
Fastify
Product
@fastify/http-proxy
Classifications
CWE-20, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 18, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <11.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Fastify · @fastify/http-proxyversion=0 <11.6.0

Published CVSS scores

10.0OpenJS FoundationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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