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MEDIUM severity

CVE-2026-47674 — hono

MEDIUMFix: honojs/hono@c831020

CVE-2026-47674 is a medium-severity (CVSS 5.3) CWE-185 vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.

Hono: IP Restriction bypasses static deny rules for non-canonical IPv6

Also known asGHSA-xrhx-7g5j-rcj5
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 16, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-47674.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs22th percentile — riskier than 22% of all scored CVEsHighest risk
0.00%0.27%0.54%0.81%0.1%0.3%Jun 26Sep 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-47674 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 390,400 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

6Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream
hononpm
74.0Mdownloads / week

Description

Summary

The ip-restriction middleware (hono/ip-restriction) compares incoming IP addresses against configured deny and allow rules using string equality after partial normalization. Non-canonical IPv6 representations of an address already listed in a static rule — such as compressed forms, explicit-zero forms, or hex-notation IPv4-mapped addresses — do not match the normalized rule entry, causing the rule to be silently skipped.

Details

When the rule matcher is built, each configured IP rule is normalized to a canonical string form. Incoming IP addresses received at request time are then compared against those canonical strings without applying the same normalization. Because IPv6 permits multiple syntactically different representations of the same numeric address, a non-canonical form of a denied address fails the string lookup and proceeds to the CIDR check, which also finds no match for rules registered as static (no prefix length). The request is then allowed.

Affected non-canonical forms include:

  • Compressed versus expanded notation (2001:db8::1 vs 2001:db8:0:0:0:0:0:1)
  • Hex-notation IPv4-mapped addresses (::ffff:7f00:1 vs ::ffff:127.0.0.1)
  • Zone identifier suffixes (e.g., fe80::1%eth0)

Additionally, invalid IP address strings provided as the remote address are not rejected and may result in unexpected allow or deny behavior.

This issue arises when applications use ipRestriction() with static (non-CIDR) rules and the IP address source can supply addresses in non-canonical IPv6 form.

Impact

A request from an IP address covered by a static deny rule may bypass the restriction if the address is presented in a non-canonical IPv6 form.

This may lead to:

  • Unauthorized access to endpoints intended to be restricted to specific IP addresses
  • Bypass of IP-based access controls in environments where the runtime or an upstream proxy provides source addresses in a form that differs from the canonical form used in the rule configuration

This issue affects applications using hono/ip-restriction with static deny rules for IPv4 or IPv6 addresses, particularly when the source address is derived from proxy headers or custom getIP implementations that may return non-canonical forms.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmhonoall versions4.12.21npm install hono@4.12.21

Affected Products

1 product · 1 configurations
Application
honohono
< 4.12.21
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hono, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update hono to 4.12.21 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-47674 is resolved across your whole dependency graph.

  3. Workarounds

    Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

### Summary The `ip-restriction` middleware (`hono/ip-restriction`) compares incoming IP addresses against configured deny and allow rules using string equality after partial normalization. Non-canonical IPv6 representations of an address already listed in a static rule — such as compressed forms, explicit-zero forms, or hex-notation IPv4-mapped addresses — do not match the normalized rule entry, causing the rule to be silently skipped. ### Details When the rule matcher is built, each configured IP rule is normalized to a canonical string form. Incoming IP addresses received at request time
O3 Security · Impact-Aware SCA

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CVE-2026-47674: hono — Fixed in 4.12.21