honojs hono up to 4.12.3 setCookie inappropriate comment style

Summaryinfo

A vulnerability, which was classified as critical, has been found in honojs hono up to 4.12.3. Affected is the function setCookie. This manipulation causes inappropriate comment style. This vulnerability appears as CVE-2026-29086. The attack may be initiated remotely. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability has been found in honojs hono up to 4.12.3 and classified as critical. Affected by this vulnerability is the function setCookie. The manipulation with an unknown input leads to a inappropriate comment style vulnerability. The CWE definition for the vulnerability is CWE-1113. The source code uses comment styles or formats that are inconsistent or do not follow expected standards for the product. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to version 4.12.4, the setCookie() utility did not validate semicolons (;), carriage returns (\r), or newline characters (\n) in the domain and path options when constructing the Set-Cookie header. Because cookie attributes are delimited by semicolons, this could allow injection of additional cookie attributes if untrusted input was passed into these fields. This issue has been patched in version 4.12.4.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-29086 since 03/03/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available.

Upgrading to version 4.12.4 eliminates this vulnerability. Applying the patch 44ae0c8cc4d5ab2bed529127a4ac72e1483ad073 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• honojs

Name

• hono

Version

• 4.12.0
• 4.12.1
• 4.12.2
• 4.12.3

License

• open-source

Website

• Product: https://github.com/honojs/hono/

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