CVE-2026-54286

On Windows hosts, an encoded backslash (%5C) in the request path decodes to \, which the Windows path resolver treats as a separator. serve-static then resolves a single URL segment such as admin\secret.txt into a nested file under the root and serves it, letting an attacker read static files meant to be protected behind prefix-mounted middleware. Directory escape (..) remains blocked.

Details

The router splits paths only on /, so /admin%5Csecret.txt is one segment and middleware on /admin/* does not run. The serve-static guard rejects ./.. and consecutive separators but lets a lone \ through; on Windows the file resolver re-splits it into the protected subtree.

This affects Windows hosts serving static files via the Node, Bun, or Deno adapters that guard a static subtree with prefix-mounted middleware.

An unauthenticated attacker can read static files under a middleware-guarded prefix on Windows hosts. The read stays within the configured root; escape outside the root is not possible.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-54286 has a CVSS score of 5.9 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.12.25); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-54286? CVE-2026-54286 is a medium-severity path traversal vulnerability in hono (npm), affecting versions < 4.12.25. It is fixed in 4.12.25. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-54286? CVE-2026-54286 has a CVSS score of 5.9 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of hono are affected by CVE-2026-54286? hono (npm) versions < 4.12.25 is affected.
4. Is there a fix for CVE-2026-54286? Yes. CVE-2026-54286 is fixed in 4.12.25. Upgrade to this version or later.
5. Is CVE-2026-54286 exploitable, and should I be worried? Whether CVE-2026-54286 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-54286 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-54286? Upgrade hono to 4.12.25 or later.