Executive brief
Hono is a popular web framework used to build fast web applications. A vulnerability in how it handles form data allows attackers to submit specially crafted input that can interfere with the application's internal logic. If the application then combines this data with other internal objects, it could lead to unauthorized data access or changes to how the application behaves.
Technical details
A prototype pollution vulnerability exists in Hono's HonoRequest.parseBody() method when the { dot: true } option is enabled. The parser fails to filter the '__proto__' path segment in form field names, allowing an attacker to construct objects containing __proto__ properties. While Hono does not modify the global Object.prototype directly, if the resulting parsed object is subsequently merged into other JavaScript objects using unsafe recursive deep merge patterns, an attacker can achieve prototype pollution. This can lead to modification of object behavior or potential bypass of security checks. The issue is fixed in version 4.12.7.
Affected products
- Hono Hono < 4.12.7
Timeline
- 2026-03-10: advisory: GitHub Security Advisory published
- 2026-07-11: disclosed: NVD publication date
- 2026-07-11: patched: Fix confirmed in version 4.12.7