What’s Vulnerable › Vulnerabilities

CVE-2026-56763: Hono - Prototype Pollution via __proto__ Key in parseBody with dot Option

• Severity: medium (CVSS 4.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-11 · updated 2026-10-25
• Weakness: CWE-1321

Description

Hono before 4.12.7 allows __proto__ key in parseBody with dot option enabled, permitting specially crafted form field names to create objects with __proto__ properties. When parsed results are merged into regular JavaScript objects using unsafe merge patterns, attackers can exploit this to achieve prototype pollution and modify object behavior.

Affected products

• honojs hono: before 4.12.7 — fixed in 4.12.7

How to fix

Upgrade to a fixed version: honojs hono 4.12.7. Check the vendor advisory for mitigations.

References

• https://github.com/honojs/hono/security/advisories/GHSA-v8w9-8mx6-g223
• https://www.vulncheck.com/advisories/hono-prototype-pollution-via-proto-key-in-parsebody-with-dot-option

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