CVE-2026-39409 — hono
Fix: honojs/hono@48fa223CVE-2026-39409 is a CWE-180 vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono has incorrect IP matching in ipRestriction() for IPv4-mapped IPv6 addresses
Exploitation Status
No confirmed exploitation observed yet
- 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-2026-39409.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
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.
hononpmDescription
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 on IPv4-based ipRestriction() rules may incorrectly allow or deny requests.
In affected deployments, a denied IPv4 client may bypass access restrictions. Conversely, legitimate clients may be rejected when using IPv4 allow lists.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.12.12npm install hono@4.12.12 |
Detection & mitigation playbook
Open-source dependencyDetect
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.
Fix
Update hono to 4.12.12 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39409 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-39409 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-39409. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-39409 in your dependencies?
O3 Security finds CVE-2026-39409 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.