CVE-2026-27700 Hono is Vulnerable to Authentication Bypass by IP Spoofing in AWS Lambda ALB conninfo
Attackers can bypass IP-based access controls in Hono applications deployed on AWS Lambda ALB by spoofing the X-Forwarded-For header.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-27700?
CVE-2026-27700 is a high-severity authentication bypass vulnerability in honojs hono, published on 25 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-27700?
2 open source packages ship an affected version, including hono. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
hono npm | From 4.12.0 | 4.12.2 |
hono npm | From 4.12.0 | 4.12.2 |
Products include Hono Hono.
How do I fix CVE-2026-27700?
Upgrade hono to 4.12.2 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-27700 being exploited?
There is no known exploitation of CVE-2026-27700 in the wild and no public exploit code.
Other vulnerabilities in honojs hono
- CVE-2026-22817 JWT Algorithm Confusion via Unsafe Default (HS256) in Hono JWT Middleware Allows Token Forgery and Auth Bypass
- CVE-2026-22818 JWT algorithm confusion in Hono JWK Auth Middleware when JWK lacks "alg" (untrusted header.alg fallback)
- CVE-2025-62610 Hono Improperly Authorizes JWT Audience Validation
- CVE-2026-29045 Hono: Arbitrary file access via serveStatic vulnerability
- CVE-2025-58362 Hono contains a flaw in URL path parsing, potentially leading to path confusion
Sources
Also known as GHSA-xh87-mx6m-69f3.