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Medium, CVSS 6.3amended

Hono has incorrect IP matching in ipRestriction() for IPv4-mapped IPv6 addresses

CVE-2026-39409GHSA-xpcf-pg52-r92g

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (hono 4.12.12), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm hono

    Affected
    < 4.12.12
    Fixed in
    4.12.12

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
6.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-39409: 0.34% estimated exploitation activity in the next 30 days; percentile 27.86 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary ipRestriction() does not canonicalize IPv4-mapped IPv6 client addresses (e.g. ::ffff:127.0.0.1) before applying IPv4 allow or deny rules. In environments such as Node.js dual-stack, this can cause IPv4 rules to fail to match, leading to unintended authorization behavior. Details The middleware classifies client addresses based on their textual form. Addresses containing ":" are treated as IPv6, including IPv4-mapped IPv6 addresses such as ::ffff:127.0.0.1. These addresses are not normalized to IPv4 before matching. As a result: IPv4 static rules (e.g. 127.0.0.1) do not match because the raw string differs IPv4 CIDR rules (e.g. 127.0.0.0/8, 10.0.0.0/8) are skipped because the address is treated as IPv6 For example, with: denyList: ['127.0.0.1'] a request from 127.0.0.1 may be represented as ::ffff:127.0.0.1 and bypass the deny rule. This behavior commonly occurs in Node.js environments where IPv4 clients are exposed as IPv4-mapped IPv6 addresses. Impact Applications that rely…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-xpcf-pg52-r92g

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-xpcf-pg52-r92g

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-39409

Advisory: Hono has incorrect IP matching in ipRestriction() for IPv4-mapped IPv6 addresses
IDs: CVE-2026-39409, GHSA-xpcf-pg52-r92g
Record: https://patchnext.com/advisories/cve-2026-39409 (revision 3, source checked 26 Oct 2026, 12:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: hono 4.12.12. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm hono: affected < 4.12.12; fixed in 4.12.12

## Suggested inspection (read-only)
- `npm ls hono --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on hono.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-xpcf-pg52-r92g (OSV record GHSA-xpcf-pg52-r92g lists affected ranges: npm hono >=0 <4.12.12 (fixed))
- Verified: https://github.com/advisories/GHSA-xpcf-pg52-r92g (GitHub-reviewed advisory GHSA-xpcf-pg52-r92g lists affected ranges: npm hono >=0 <4.12.12)

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