Summary
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.
Details
setCookie() builds the Set-Cookie header by concatenating option values. While the cookie value itself is URL-encoded, the domain and path options were previously interpolated without rejecting unsafe characters.
Including ;, \r, or \n in these fields could result in unintended additional attributes (such as SameSite, Secure, Domain, or Path) being appended to the cookie header.
Modern runtimes prevent full header injection via CRLF, so this issue is limited to attribute-level manipulation within a single Set-Cookie header.
The issue has been fixed by rejecting these characters in the domain and path options.
Impact
An attacker may be able to manipulate cookie attributes if an application passes user-controlled input directly into the domain or path options of setCookie().
This could affect cookie scoping or security attributes depending on browser behavior. Exploitation requires application-level misuse of cookie options.
CVE-2026-29086 has a CVSS score of 5.4 (Medium). The vector is network-reachable, no privileges required, and user interaction required. 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 (4.12.4); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-29086? CVE-2026-29086 is a medium-severity security vulnerability in hono (npm), affecting versions < 4.12.4. It is fixed in 4.12.4.
- How severe is CVE-2026-29086? CVE-2026-29086 has a CVSS score of 5.4 (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.
- Which versions of hono are affected by CVE-2026-29086? hono (npm) versions < 4.12.4 is affected.
- Is there a fix for CVE-2026-29086? Yes. CVE-2026-29086 is fixed in 4.12.4. Upgrade to this version or later.
- Is CVE-2026-29086 exploitable, and should I be worried? Whether CVE-2026-29086 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
- What actually determines whether CVE-2026-29086 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.
- How do I fix CVE-2026-29086? Upgrade
honoto 4.12.4 or later.