GHSA-26PP-8WGV-HJVM

Cookie names are not validated on the write path when using setCookie(), serialize(), or serializeSigned() to generate Set-Cookie headers.

While certain cookie attributes such as domain and path are validated, the cookie name itself may contain invalid characters.

This results in inconsistent handling of cookie names between parsing (read path) and serialization (write path).

Details

When applications use setCookie(), serialize(), or serializeSigned() with a user-controlled cookie name, invalid values (e.g., containing control characters such as \r or \n) can be used to construct malformed Set-Cookie header values.

For example:

Set-Cookie: legit
X-Injected: evil=value

However, in modern runtimes such as Node.js and Cloudflare Workers, such invalid header values are rejected and result in a runtime error before the response is sent.

As a result, the reported header injection / response splitting behavior could not be reproduced in these environments.

Applications that pass untrusted input as the cookie name to setCookie(), serialize(), or serializeSigned() may encounter runtime errors due to invalid header values.

In tested environments, malformed Set-Cookie headers are rejected before being sent, and the reported header injection behavior could not be reproduced.

This issue primarily affects correctness and robustness rather than introducing a confirmed exploitable vulnerability.

GHSA-26PP-8WGV-HJVM has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.12.12); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is GHSA-26PP-8WGV-HJVM? GHSA-26PP-8WGV-HJVM is a medium-severity security vulnerability in hono (npm), affecting versions < 4.12.12. It is fixed in 4.12.12.
2. How severe is GHSA-26PP-8WGV-HJVM? GHSA-26PP-8WGV-HJVM has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of hono are affected by GHSA-26PP-8WGV-HJVM? hono (npm) versions < 4.12.12 is affected.
4. Is there a fix for GHSA-26PP-8WGV-HJVM? Yes. GHSA-26PP-8WGV-HJVM is fixed in 4.12.12. Upgrade to this version or later.
5. Is GHSA-26PP-8WGV-HJVM exploitable, and should I be worried? Whether GHSA-26PP-8WGV-HJVM is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether GHSA-26PP-8WGV-HJVM is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix GHSA-26PP-8WGV-HJVM? Upgrade hono to 4.12.12 or later.