# 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.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **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:** Yes
- **Published:** 12 Nov 2026
- **Updated:** 12 Nov 2026
- **Also known as:** GHSA-jpvv-r467-5p4w

## 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 (Interpretation Conflict)

## 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 | Ecosystem | 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.

## Is CVE-2026-126210 being exploited?

There is no known exploitation of CVE-2026-126210 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126210 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-126210 in the wild and no public exploit code.
Exposure: An affected version is exposed as installed. No special setting or call is needed.

Affected packages and fixed versions:
- @hono/node-server (npm): affected all versions; fixed in 1.19.18
- @hono/node-server (npm): affected from 2.0.0; fixed in 2.1.6

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-126210/ (Markdown: https://insights.sbomify.com/CVE-2026-126210/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126210
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126210
- OSV: https://osv.dev/vulnerability/CVE-2026-126210

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126210/
Summaries are generated and may contain mistakes; the official description above is the record.