Is there a public exploit for CVE-2026-126357?

No public exploit for CVE-2026-126357 was found in Exploit-DB, Metasploit, Nuclei templates or public proof-of-concept repositories. That is an absence of evidence rather than proof that none exists.

How severe is CVE-2026-126357?

CVE-2026-126357 scores CVSS 5.3 (v3.1), rated medium. EPSS puts the chance of exploitation in the next 30 days at 0.004%.

5.3 Medium

Hono: `mount()` and `app.mount()` can forward a path that bypasses middleware scoped inside the mount prefix

CVE-2026-126357

Summary mount() and app.mount() remove the mount prefix from the request path and forward the rest to the mounted application. Two mistakes in that step let a crafted request reach a route of the mounted application that the outer application protects with path-scoped middleware, such as an authentication check on /app/admin/. The outer application routes on the original path, so the middleware does not run. Details 1. Dynamic prefix (all affected versions): for a mount such as /api/:tenant/, the prefix was removed by the length of the route pattern, not of the matched prefix. A request with a longer or shorter first segment is cut in the middle, so /api/a/xxxxx/admin/secret reaches the mounted application as /admin/secret. 2. Re-normalization (since 4.12.21): the forwarded path was built from the decoded request path and assigned to url.pathname, which turns a decoded backslash into / and collapses ... /app/public%5C..%5Cadmin/secret reaches the mounted application as /admin/secret. The fix removes the prefix segment by segment from the raw pathname, using the matched parameter values for its length. Route patterns that cannot be handled safely now throw: duplicate parameter…

Assessment

CVSS: 5.3 (v3.1)
Severity: Medium
EPSS: 0.004% chance of exploitation in the next 30 days
Known exploited: Not listed in CISA KEV
Exploit availability: Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
Published: 12 November 2026
Last updated: 12 November 2026
Affected: hono
Weakness: CWE-288

CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

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