Vulnerability · Published May 28, 2026 · Assigned by GitHub_M

CVE-2026-47676Hono: app.mount() strips mount prefix using undecoded path, causing incorrect routing for percent-encoded paths

Medium 5.3

In plain English

A medium-severity security flaw 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 18% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium

Exploit odds (30 days)0.3%top 82.3% 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 4.12.21, app.mount() strips the mount prefix from the incoming request path using the raw URL pathname, while route matching is performed against the percent-decoded path. This inconsistency causes the prefix to be stripped at the wrong position when the path contains percent-encoded multi-byte characters, resulting in the mounted sub-application receiving an incorrect path. This vulnerability is fixed in 4.12.21.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	hono	4.12.21	GHSA-2gcr-mfcq-wcc3

Affected products (as reported)

Vendor	Product	Versions
honojs	hono	< 4.12.21

Weakness: CWE-444, CWE-693 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

References

https://github.com/honojs/hono/security/advisories/GHSA-2gcr-mfcq-wcc3 x_refsource_CONFIRM