CVE-2026-126356
Hono: `validator('form')` skips validation for `multipart/form-data` requests with extra parameters
- Medium 5.3
Description
Hono is a Web application framework that provides support for any JavaScript runtime. From 4.5.1 until 4.13.16, validator('form') uses a strict whole-header pattern that fails to recognize multipart/form-data when its Content-Type includes another legal parameter or extra whitespace after a semicolon. The validation callback receives an empty object even though c.req.parseBody() or c.req.formData() can still parse and expose all submitted fields to the handler. An unauthenticated client can therefore bypass allow-list or required-field checks when the application relies on the form validator and its callback accepts an empty object. application/x-www-form-urlencoded requests are not affected. This issue is fixed in version 4.13.16.
Key facts
- Published
- 12 Nov 2026
- Last changed
- 13 Nov 2026
- Assigned by
- GitHub_M
- EPSS
- 0.392% likely to be exploited in the next 30 days, higher than 33.878% of CVEs (scores for 15 Nov 2026)
- SSVC (CISA)
- Exploitation: none; Automatable: yes; Technical impact: partial
Severity scores
Each score is shown as its source gave it. They are not averaged or merged.
- 5.3CVSS 3.1, Mediumfrom the CNA (GitHub_M)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Historical context and remediation
This reference retains the original CVE publication date. A recent record update does not mean a new attack occurred.
No separately sourced impact summary is available on this page yet. Consult the description, version data and dated exploitation evidence.
No explicit remediation statement is available on this page yet. Consult the original record and vendor references before choosing a fix.
Version statuses below come from the CNA. An “unaffected” version is not necessarily a currently supported release or proof of a patch date. EPSS is a dated risk estimate, not a count of historical attacks.
Affected products
| Vendor | Product | Versions |
|---|---|---|
| honojs | hono |
|
Timeline
- 12 Nov 2026 Published