CVE-2026-29086 is a medium-severity (CVSS 5.4) CWE-1113 vulnerability in hono. O3 Security confirms whether CVE-2026-29086 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Hono: Cookie Attribute Injection via Unsanitized domain and path in setCookie()
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
hononpmDescription
Hono is a Web application framework that provides support for any JavaScript runtime. Prior to version 4.12.4, the setCookie() utility did not validate semicolons (;), carriage returns (\r), or newline characters (\n) in the domain and path options when constructing the Set-Cookie header. Because cookie attributes are delimited by semicolons, this could allow injection of additional cookie attributes if untrusted input was passed into these fields. This issue has been patched in version 4.12.4.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.12.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hono. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update hono to 4.12.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-29086 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 pinpoints whether CVE-2026-29086 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-29086. 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-2026-29086 in your dependencies?
O3 detects CVE-2026-29086 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.