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.

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

EPSS: 0.003 (19.1th percentile) — read the EPSS interpretation.

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.

Affected products

Hono — versions 0, 4.12.7

Weakness classification (CWE)

CWE-1321 — Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution)

References

disclosure@vulncheck.com (vendor-advisory)
disclosure@vulncheck.com (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.