CVE-2026-56762: Hono - Missing Cookie Name Validation in setCookie()

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-23 · updated 2026-06-24
Weakness: CWE-20

Description

Hono before 4.12.12 does not validate cookie names on the write path in the setCookie(), serialize(), and serializeSigned() functions, allowing invalid characters such as control characters (e.g. \r or \n) when an application passes a user-controlled cookie name. This can produce malformed Set-Cookie header values. In modern runtimes such as Node.js and Cloudflare Workers, such invalid header values are rejected and cause a runtime error before the response is sent, so header injection or response splitting could not be reproduced; the issue primarily affects correctness and robustness, resulting in runtime errors (availability) rather than confirmed header injection.

Affected products

honojs hono: before 4.12.12 — fixed in 4.12.12

How to fix

Upgrade to a fixed version: honojs hono 4.12.12. Check the vendor advisory for mitigations.

References

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