CVE-2026-47674

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.

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.

CVE-2026-47674 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.12.21); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-47674? CVE-2026-47674 is a medium-severity security vulnerability in hono (npm), affecting versions < 4.12.21. It is fixed in 4.12.21.
2. How severe is CVE-2026-47674? CVE-2026-47674 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of hono are affected by CVE-2026-47674? hono (npm) versions < 4.12.21 is affected.
4. Is there a fix for CVE-2026-47674? Yes. CVE-2026-47674 is fixed in 4.12.21. Upgrade to this version or later.
5. Is CVE-2026-47674 exploitable, and should I be worried? Whether CVE-2026-47674 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-47674 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-47674? Upgrade hono to 4.12.21 or later.