# CVE-2026-56762: Hono - Missing Cookie Name Validation in setCookie()

> Attackers can cause runtime errors and denial of service by passing invalid characters in user-controlled cookie names to the Hono web framework.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Jun 2026
- **Updated:** 24 Jun 2026
- **Also known as:** CLEANSTART-2026-NV57735, GHSA-26pp-8wgv-hjvm, MINI-87w7-2pjv-9x5p, MINI-cqrj-rf6g-v432, MINI-m6p6-3gwx-vgxf, MINI-p553-f29r-v33g, MINI-p8q8-47jc-f5f2, MINI-pvv9-4r7w-r35f, MINI-r39v-9qxq-4jgm

## What is CVE-2026-56762?

CVE-2026-56762 is a medium-severity vulnerability in Hono, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Hono before 4.12.12 does not validate cookie names on the write path in the setCookie(), serialize(), and serializeSigned() functions, allowing invalid characters such as control characters (e.g. \r or \n) when an application passes a user-controlled cookie name. This can produce malformed Set-Cookie header values. In modern runtimes such as Node.js and Cloudflare Workers, such invalid header values are rejected and cause a runtime error before the response is sent, so header injection or response splitting could not be reproduced; the issue primarily affects correctness and robustness, resulting in runtime errors (availability) rather than confirmed header injection.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-56762?

2 open source packages ship an affected version, including hono.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hono` | npm | All versions | 4.12.12 |
| `hono` | npm | All versions | 4.12.12 |

## How do I fix CVE-2026-56762?

Upgrade hono to 4.12.12 or later.

## Is CVE-2026-56762 being exploited?

There is no known exploitation of CVE-2026-56762 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-56762 and fix it if it is affected.

What it is: CVE-2026-56762 is a medium-severity vulnerability in Hono, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-56762 in the wild and no public exploit code.

Affected packages and fixed versions:
- hono (npm): affected all versions; fixed in 4.12.12
- hono (npm): affected all versions; fixed in 4.12.12

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-56762/ (Markdown: https://insights.sbomify.com/CVE-2026-56762/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-56762
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56762
- OSV: https://osv.dev/vulnerability/CVE-2026-56762

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-56762/
Summaries are generated and may contain mistakes; the official description above is the record.