CVE-2026-27700 is a high-severity (CVSS 8.2) CWE-290 vulnerability in hono. O3 Security confirms whether CVE-2026-27700 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Hono is Vulnerable to Authentication Bypass by IP Spoofing in AWS Lambda ALB conninfo
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. In versions 4.12.0 and 4.12.1, when using the AWS Lambda adapter (hono/aws-lambda) behind an Application Load Balancer (ALB), the getConnInfo() function incorrectly selected the first value from the X-Forwarded-For header. Because AWS ALB appends the real client IP address to the end of the X-Forwarded-For header, the first value can be attacker-controlled. This could allow IP-based access control mechanisms (such as the ipRestriction middleware) to be bypassed. Version 4.12.2 patches the issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | ≥ 4.12.0&&< 4.12.2 | 4.12.2 |
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 4.12.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27700 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-2026-27700 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-2026-27700. 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-2026-27700 in your dependencies?
O3 detects CVE-2026-27700 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.