CVE-2026-47675

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.21, the serialize() function in hono/cookie validates domain and path options against characters that corrupt Set-Cookie header syntax (;, \r, \n), but does not apply the same validation to sameSite and priority. An application that passes user-controlled input into either option may produce a Set-Cookie response header containing attacker-chosen additional attributes. This vulnerability is fixed in 4.12.21.

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.21, the serialize() function in hono/cookie validates domain and path options against characters that corrupt Set-Cookie header syntax (;, \r, \n), but does not apply the same validation to sameSite and priority. An application that passes user-controlled input into either option may produce a Set-Cookie response header containing attacker-chosen additional attributes. This vulnerability is fixed in 4.12.21.

Summary

The serialize() function in hono/cookie validates domain and path options against characters that corrupt Set-Cookie header syntax (;, \r, \n), but does not apply the same validation to sameSite and priority. An application that passes user-controlled input into either option may produce a Set-Cookie response header containing attacker-chosen additional attributes.

Details

When constructing a Set-Cookie header value, serialize() appends the sameSite and priority option values directly into the output string after a presentation-only transformation (capitalizing the first character). Although the TypeScript type signature constrains these options to specific string literals, that constraint is not enforced at runtime; any string value, including one containing ; or line-feed characters, passes through unchanged.

The validation guard that rejects ;, \r, and \n from domain and path is not applied to sameSite or priority. An application that passes a request-derived value to either option therefore provides an injection point into the header line.

This issue arises when an application passes user-controlled input to the sameSite or priority option of setCookie() or serialize().

Impact

An attacker who can control the sameSite or priority option value may inject additional attributes into a Set-Cookie response header.

This may lead to:

• Cookie attribute injection — overriding Domain, Path, HttpOnly, Secure, or Max-Age for the affected cookie
• HTTP response header injection on runtimes that do not strictly validate header values, enabling a second attacker-controlled Set-Cookie header in the same response

This issue affects applications that pass user-derived input into the sameSite or priority option of hono/cookie serialization functions.

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.21, the serialize() function in hono/cookie validates domain and path options against characters that corrupt Set-Cookie header syntax (;, \r, \n), but does not apply the same validation to sameSite and priority. An application that passes user-controlled input into either option may produce a Set-Cookie response header containing attacker-chosen additional attributes. This vulnerability is fixed in 4.12.21.

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.21, the serialize() function in hono/cookie validates domain and path options against characters that corrupt Set-Cookie header syntax (;, \r, \n), but does not apply the same validation to sameSite and priority. An application that passes user-controlled input into either option may produce a Set-Cookie response header containing attacker-chosen additional attributes. This vulnerability is fixed in 4.12.21.

Summary

The serialize() function in hono/cookie validates domain and path options against characters that corrupt Set-Cookie header syntax (;, \r, \n), but does not apply the same validation to sameSite and priority. An application that passes user-controlled input into either option may produce a Set-Cookie response header containing attacker-chosen additional attributes.

Details

When constructing a Set-Cookie header value, serialize() appends the sameSite and priority option values directly into the output string after a presentation-only transformation (capitalizing the first character). Although the TypeScript type signature constrains these options to specific string literals, that constraint is not enforced at runtime; any string value, including one containing ; or line-feed characters, passes through unchanged.

The validation guard that rejects ;, \r, and \n from domain and path is not applied to sameSite or priority. An application that passes a request-derived value to either option therefore provides an injection point into the header line.

This issue arises when an application passes user-controlled input to the sameSite or priority option of setCookie() or serialize().

Impact

An attacker who can control the sameSite or priority option value may inject additional attributes into a Set-Cookie response header.

This may lead to:

• Cookie attribute injection — overriding Domain, Path, HttpOnly, Secure, or Max-Age for the affected cookie
• HTTP response header injection on runtimes that do not strictly validate header values, enabling a second attacker-controlled Set-Cookie header in the same response

This issue affects applications that pass user-derived input into the sameSite or priority option of hono/cookie serialization functions.

TuxCare rebuilt hono to address 12 CVEs. Fixed in 3.12.12-tuxcare.2.

Root has patched CVE-2026-47675 in the @rootio/hono package for Root:npm. Multiple fixed versions available.