CVE-2026-27700
📋 TL;DR
This vulnerability in Hono framework versions 4.12.0-4.12.1 allows attackers to bypass IP-based access controls when using the AWS Lambda adapter behind an Application Load Balancer. By manipulating the X-Forwarded-For header, attackers can spoof their IP address to appear as trusted. This affects any Hono application deployed on AWS Lambda with ALB that uses IP restriction middleware.
💻 Affected Systems
- Hono
📦 What is this software?
Hono by Hono
⚠️ Risk & Real-World Impact
Worst Case
Complete bypass of IP-based authentication and authorization controls, allowing unauthorized access to protected endpoints and potential data exposure.
Likely Case
Attackers bypass IP whitelisting/blacklisting to access restricted API endpoints or administrative interfaces.
If Mitigated
Limited impact if additional authentication layers exist beyond IP-based controls.
🎯 Exploit Status
Exploitation requires ability to send HTTP requests with manipulated X-Forwarded-For headers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.12.2
Vendor Advisory: https://github.com/honojs/hono/security/advisories/GHSA-xh87-mx6m-69f3
Restart Required: Yes
Instructions:
1. Update Hono package to version 4.12.2 or later using npm/yarn/pnpm. 2. Deploy updated application. 3. Restart Lambda functions.
🔧 Temporary Workarounds
Custom IP extraction middleware
allImplement custom middleware to correctly extract client IP from X-Forwarded-For header when using AWS ALB
// Example: Extract last IP from X-Forwarded-For header
app.use('*', async (c, next) => {
const xff = c.req.header('X-Forwarded-For');
if (xff) {
const ips = xff.split(',').map(ip => ip.trim());
c.set('client-ip', ips[ips.length - 1]);
}
await next();
})
🧯 If You Can't Patch
- Implement additional authentication layers beyond IP-based controls
- Use AWS WAF to validate X-Forwarded-For headers at the ALB level
🔍 How to Verify
Check if Vulnerable:
Check if using Hono 4.12.0 or 4.12.1 with AWS Lambda adapter behind ALB and IP-based access controls.Check Version:
npm list hono | grep honoVerify Fix Applied:
Verify Hono version is 4.12.2 or later and test IP restriction functionality with manipulated X-Forwarded-For headers.📡 Detection & Monitoring
Log Indicators:
- Requests with multiple IPs in X-Forwarded-For header
- Access from unexpected IP addresses to restricted endpoints
Network Indicators:
- HTTP requests with manipulated X-Forwarded-For headers
SIEM Query:
http.headers.x_forwarded_for:* AND (http.status:403 OR http.status:200) AND NOT http.headers.x_forwarded_for:/(^[^,]+$)/