CVE-2026-54286 Hono: Path traversal in `serve-static` on Windows via encoded backslash (`%5C`)
Attackers can read protected static files on Windows hosts by using encoded backslashes in request paths, bypassing prefix-mounted middleware restrictions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-54286?
CVE-2026-54286 is a medium-severity path traversal vulnerability in honojs hono, published on 22 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.25, 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. This vulnerability is fixed in 4.12.25.
Weakness: CWE-22
Which versions are affected by CVE-2026-54286?
2 open source packages ship an affected version, including hono.
| Package | Affected | Fixed in |
|---|---|---|
hono npm | All versions | 4.12.25 |
hono npm | All versions | 4.12.25 |
How do I fix CVE-2026-54286?
Upgrade hono to 4.12.25 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-54286 being exploited?
There is no known exploitation of CVE-2026-54286 in the wild and no public exploit code.
Sources
Also known as ECHO-d407-4169-3fe7, GHSA-wwfh-h76j-fc44, MINI-5f7j-4cwp-hp56, MINI-72rc-4r52-9p4p, MINI-96c2-c8cj-55xh, MINI-9whp-hqm8-57fr and 9 more.