CVE-2026-56762 — hono
Fix: honojs/hono@a586cd7CVE-2026-56762 is a Improper Input Validation vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono - Missing Cookie Name Validation in setCookie()
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- 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-2026-56762.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
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
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.
Impact
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.12.12npm install hono@4.12.12 |
Detection & 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 4.12.12 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-56762 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-2026-56762 in your dependencies?
Find it across npm, including transitive dependencies.