# 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.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Feb 2026
- **Updated:** 27 Feb 2026
- **Also known as:** GHSA-xh87-mx6m-69f3

## 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.

Weakness: CWE-345 (Insufficient Verification of Data Authenticity), CWE-290 (Authentication Bypass by Spoofing)

## Which versions are affected by CVE-2026-27700?

2 open source packages ship an affected version, including hono. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hono` | npm | From 4.12.0 | 4.12.2 |
| `hono` | npm | From 4.12.0 | 4.12.2 |

Products: Hono Hono.

## How do I fix CVE-2026-27700?

Upgrade hono to 4.12.2 or later.

## 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](https://insights.sbomify.com/CVE-2026-22817/): JWT Algorithm Confusion via Unsafe Default (HS256) in Hono JWT Middleware Allows Token Forgery and Auth Bypass (high 8.2)
- [CVE-2026-22818](https://insights.sbomify.com/CVE-2026-22818/): JWT algorithm confusion in Hono JWK Auth Middleware when JWK lacks "alg" (untrusted header.alg fallback) (high 8.2)
- [CVE-2025-62610](https://insights.sbomify.com/CVE-2025-62610/): Hono Improperly Authorizes JWT Audience Validation (high 8.1)
- [CVE-2026-29045](https://insights.sbomify.com/CVE-2026-29045/): Hono: Arbitrary file access via serveStatic vulnerability (high 7.5)
- [CVE-2025-58362](https://insights.sbomify.com/CVE-2025-58362/): Hono contains a flaw in URL path parsing, potentially leading to path confusion (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-27700 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-27700 in the wild and no public exploit code.

Affected packages and fixed versions:
- hono (npm): affected from 4.12.0; fixed in 4.12.2
- hono (npm): affected from 4.12.0; fixed in 4.12.2

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-27700/ (Markdown: https://insights.sbomify.com/CVE-2026-27700/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27700
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27700
- OSV: https://osv.dev/vulnerability/CVE-2026-27700

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27700/
Summaries are generated and may contain mistakes; the official description above is the record.