Description
@fastify/proxy-addr is a Fastify plugin that determines a request's client address behind trusted reverse proxies, and it backs Fastify request.ip and request.ips. In versions 3.0.0 through 5.1.0, a trust subnet written in IPv4-mapped IPv6 notation with an IPv4-sized prefix, such as ::ffff:10.0.0.0/8 instead of the correct ::ffff:10.0.0.0/104, is accepted without error but trusts every IPv4 address on the internet rather than the block it names. Because the socket peer then becomes trusted at hop 0, any unauthenticated client can supply an arbitrary X-Forwarded-For header and control the address the application reads, which defeats IP-based access control, rate limiting, geolocation, and audit logging. The plugin inherited this defect from the upstream proxy-addr module (CVE-2026-90711). The issue is fixed in @fastify/proxy-addr 5.1.1, and users should upgrade to 5.1.1 or later. As a workaround, ensure any IPv4-mapped IPv6 trust subnet uses a prefix length of at least 97, or express the range in plain IPv4 notation.
Published: 2026-09-16
Score: 9.1 Critical
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
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Remediation

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History

Thu, 17 Sep 2026 20:30:00 +0000

Type Values Removed Values Added
First Time appeared Fastify
Fastify proxy-addr
Vendors & Products Fastify
Fastify proxy-addr

Thu, 17 Sep 2026 19:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Wed, 16 Sep 2026 14:45:00 +0000

Type Values Removed Values Added
Description @fastify/proxy-addr is a Fastify plugin that determines a request's client address behind trusted reverse proxies, and it backs Fastify request.ip and request.ips. In versions 3.0.0 through 5.1.0, a trust subnet written in IPv4-mapped IPv6 notation with an IPv4-sized prefix, such as ::ffff:10.0.0.0/8 instead of the correct ::ffff:10.0.0.0/104, is accepted without error but trusts every IPv4 address on the internet rather than the block it names. Because the socket peer then becomes trusted at hop 0, any unauthenticated client can supply an arbitrary X-Forwarded-For header and control the address the application reads, which defeats IP-based access control, rate limiting, geolocation, and audit logging. The plugin inherited this defect from the upstream proxy-addr module (CVE-2026-90711). The issue is fixed in @fastify/proxy-addr 5.1.1, and users should upgrade to 5.1.1 or later. As a workaround, ensure any IPv4-mapped IPv6 trust subnet uses a prefix length of at least 97, or express the range in plain IPv4 notation.
Title @fastify/proxy-addr vulnerable to IP spoofing via IPv4-mapped IPv6 trust subnet
Weaknesses CWE-290
CWE-348
CWE-697
References
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'}


Subscriptions

Fastify Proxy-addr
cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-09-17T18:39:20.231Z

Reserved: 2026-09-16T08:28:17.064Z

Link: CVE-2026-92395

cve-icon Vulnrichment

Updated: 2026-09-17T18:39:12.885Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-09-16T15:19:01.857

Modified: 2026-09-17T19:17:07.053

Link: CVE-2026-92395

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-17T19:50:05Z

Weaknesses
  • CWE-290

    Authentication Bypass by Spoofing

  • CWE-348

    Use of Less Trusted Source

  • CWE-697

    Incorrect Comparison