Is CVE-2026-39409 in the CISA KEV catalog?

No. CVE-2026-39409 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-39409?

CVE-2026-39409 has a CVSS v3 base score of 5.3 (MEDIUM).

What is the EPSS score for CVE-2026-39409?

CVE-2026-39409 has an EPSS score of 0.34% (26th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix or mitigate CVE-2026-39409?

No published fix for CVE-2026-39409 has been found yet. Check the linked vendor advisories for guidance as it becomes available.

CVE & CISA-KEV Catalog

CVE-2026-39409

MEDIUM

5.3

CVSS v3

NVD

Description

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.12, 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. This vulnerability is fixed in 4.12.12.

CWE-180

How to fix

No published remediation has been found for this vulnerability's affected products yet.

Mitigation guidance may be in the linked vendor advisories in the References section below.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityLow

IntegrityNone

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Exploit Intelligence

0.34%probability of exploitation in 30 days

26thpercentile

Low risk: more likely to be exploited than 26% of all known CVEs.

References

Patch1

github.com

Vendor Advisory1

github.com

Release Notes1

github.com

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-21.