IP Address Bypass in Hono Web Application Framework Versions 4.12.0 and 4.12.1

CVE-2026-27700

What is CVE-2026-27700?

CVE-2026-27700 is a vulnerability identified in the Hono web application framework, which supports various JavaScript runtimes. This specific flaw affects versions 4.12.0 and 4.12.1 when using the AWS Lambda adapter in conjunction with an Application Load Balancer (ALB). The vulnerability is rooted in the getConnInfo() function, which incorrectly processes the X-Forwarded-For header by selecting the first value instead of considering the entire list. The critical aspect is that AWS ALB appends the actual client IP address to the end of this header, making it susceptible to manipulation by attackers. By exploiting this vulnerability, attackers can bypass IP-based access controls, such as the ipRestriction middleware, which could lead to unauthorized access and potential compromise of sensitive resources.

Potential impact of CVE-2026-27700

1. Bypass of Access Controls: The primary risk posed by this vulnerability is the ability for malicious actors to bypass established IP-based access control mechanisms. This undermines the security protocols that organizations rely on to protect sensitive applications and data.

2. Increased Attack Surface: With the ability to manipulate client IP detection, the vulnerability expands the attack surface available to threat actors. This can lead to a higher likelihood of unauthorized access attempts and successful compromises.

3. Compromise of Sensitive Data: If attackers successfully exploit this vulnerability, they may gain access to sensitive information or critical application functions, leading to data breaches and potentially significant financial or reputational damage to organizations.

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