Unauthenticated route bypass via raw-path prefix slicing
Published May 28, 2026 · Updated May 28, 2026
Routing confusion in Hono before 4.12.21 allows remote attackers to reach unintended mounted handlers via percent-encoded paths. The app.mount() method calculates a decoded prefix length but slices that count from the raw URL pathname, whose encoded multibyte characters occupy more positions. Applications using app.mount() with encoded characters in the mount prefix or request path can bypass intended middleware or route matching and expose unintended sub-application handlers.
Summary
What happened
Routing confusion in Hono before 4.12.21 allows remote attackers to reach unintended mounted handlers via percent-encoded paths. The app.mount() method calculates a decoded prefix length but slices that count from the raw URL pathname, whose encoded multibyte characters occupy more positions. Applications using app.mount() with encoded characters in the mount prefix or request path can bypass intended middleware or route matching and expose unintended sub-application handlers.
The record
- CVE
- CVE-2026-47676
- Published
- May 28, 2026
- Updated
- May 28, 2026
- Vendor
- Hono
- Product
- Hono
- Classifications
- CWE-693, CWE-444, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 28, 2026CVE publishedPublication date reported by the CVE source.
- May 28, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=< 4.12.21
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
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Your stack
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