GHSA-wwfh-h76j-fc44 hono: Path traversal in `serve-static` on Windows via encoded backslash (`%5C`)

• npm hono: < 4.12.25 → fixed in 4.12.25

Summary 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. Impact 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.