Incorrect Behavior Order: Validate Before Canonicalize in hono - CVE-2026-39409
Published: July 24, 2026
Vulnerability identifier: #VU139308
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-39409
CWE-ID: CWE-180
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass IP-based access restrictions.
The vulnerability exists due to incorrect behavior order: validate before canonicalize in ipRestriction() when processing IPv4-mapped IPv6 client addresses against IPv4 allow or deny rules. A remote attacker can send requests from an IPv4 address represented as an IPv4-mapped IPv6 address to bypass IP-based access restrictions.
This issue occurs in dual-stack environments where IPv4 clients may be represented as IPv4-mapped IPv6 addresses.
Affected software
hono
How to mitigate CVE-2026-39409
Install security update from vendor's website.
hono - update to 4.12.12