CVE-2026-29086 is a medium-severity (CVSS 5.4) CWE-1113 vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono: Cookie Attribute Injection via Unsanitized domain and path in setCookie()
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-29086.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
hononpmDescription
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.12.4npm install hono@4.12.4 |
Affected Products
honohonoDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hono, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hono to 4.12.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-29086 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-29086 in your dependencies?
Find it across npm, including transitive dependencies.