CVE-2026-126210 @hono/node-server: Backslash in the request path is parsed as a path separator, bypassing path-based access control at a reverse proxy
Unauthenticated clients can use backslashes in request paths to reach routes blocked by upstream reverse proxies or WAFs; Hono Node.js app operators should care.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Harmful if only installed
- No
- Needs a specific call
- No
- Fix
- Available
What is CVE-2026-126210?
CVE-2026-126210 is a medium-severity security feature bypass vulnerability in honojs node-server, published on 12 Nov 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
@hono/node-server allows running the Hono application on Node.js. Prior to 1.19.18 and from 2.0.0 until 2.1.6, the server passes a raw request-target containing a backslash in its path to the WHATWG URL parser, which treats the backslash as a path separator and resolves dot segments. A reverse proxy, load balancer, or web application firewall that preserves the backslash and applies path-based rules to the original request can therefore permit a request that the application normalizes to a blocked route. This lets an unauthenticated client reach route content that the upstream component was intended to deny, while Hono application access controls are unaffected because they operate on the normalized path. This issue is fixed in versions 1.19.18 and 2.1.6.
Weakness: CWE-436
Which versions are affected by CVE-2026-126210?
2 open source packages ship an affected version, including @hono/node-server.
An affected version is exposed as installed. No special setting or call is needed.
| Package | Affected | Fixed in |
|---|---|---|
@hono/node-server npm | All versions | 1.19.18 |
@hono/node-server npm | From 2.0.0 | 2.1.6 |
How do I fix CVE-2026-126210?
Upgrade @hono/node-server to a fixed version for your release line: 1.19.18 or 2.1.6.
Upgrade to the fixed version, and do not rely on a single control for protection. More about Security feature bypass.
Is CVE-2026-126210 being exploited?
There is no known exploitation of CVE-2026-126210 in the wild and no public exploit code.
Sources
Also known as GHSA-jpvv-r467-5p4w.