Vulnerability · Published Apr 8, 2026 · Assigned by GitHub_M

CVE-2026-39410Hono has a non-breaking space prefix bypass in cookie name handling in getCookie()

Medium 4.8

In plain English

A medium-severity improper input validation in hono from honojs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 22% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.8Medium

Exploit odds (30 days)0.3%top 78.5% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.12, a discrepancy between browser cookie parsing and parse() handling allows cookie prefix protections to be bypassed. Cookie names that are treated as distinct by the browser may be normalized to the same key by parse(), allowing attacker-controlled cookies to override legitimate ones. This vulnerability is fixed in 4.12.12.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	hono	4.12.12	GHSA-r5rp-j6wh-rvv4

Affected products (as reported)

Vendor	Product	Versions
honojs	hono	< 4.12.12

Weakness: CWE-20 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

References

https://github.com/honojs/hono/security/advisories/GHSA-r5rp-j6wh-rvv4 x_refsource_CONFIRM
https://github.com/honojs/hono/commit/cc067c85592415cb1880ad3c61ed923472452ec0 x_refsource_MISC
https://github.com/honojs/hono/releases/tag/v4.12.12 x_refsource_MISC