Prototype Pollution in Hono
CVE-2026-56763
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.
Vulnerability class: Prototype Pollution
Published · last modified .
CVSS v3 metric
CVSS v3 base score 4.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (18.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 18th percentile — 18.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000
Affected products
- Hono — versions 0, 4.12.7
Weakness classification (CWE)
References
- github.com/honojs/hono/security/advisories/GHSA-v8w9-8mx6-g223 (vendor-advisory)
- www.vulncheck.com/advisories/hono-prototype-pollution-via-proto-key-in-parsebod… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-56763?
- CVE-2026-56763 is a medium-severity vulnerability in Hono, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 4.8/10. Published 2026-07-11.
- How severe is CVE-2026-56763?
- Medium severity. CVSS v3 base score is 4.8 out of 10.