CVE-2026-84363 Hono: Query parser reads parameters after the URL fragment, causing cache-key and proxy interpretation differentials
Hono framework mishandles query parameters after URL fragments, allowing cache poisoning, filtering bypass, and potential XSS in specific runtime environments.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-84363?
CVE-2026-84363 is a medium-severity vulnerability in honojs hono, published on 1 Sep 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 4.13.5, Hono's query helpers treat a question mark after a literal hash fragment as the start of a query string, so the application can read request parameters that browsers, new URL(), reverse proxies, filtering rules, parameter allow and deny lists, access logging, request validation, and other middleware do not observe. The Cache Middleware removes the fragment when building its cache key, allowing a response influenced by parameters inside the fragment to be stored under a key that omits those parameters and later served to other users. This can bypass filtering and auditing, poison cached responses, and enable stored cross-site scripting when an affected parameter is reflected into cached HTML without escaping. Exploitation requires a runtime and intermediary path that passes a literal hash character through to the request URL; Cloudflare Workers and intermediaries that strip fragments are not affected. This issue is fixed in version 4.13.5.
Weakness: CWE-444
Which versions are affected by CVE-2026-84363?
2 open source packages ship an affected version, including hono.
| Package | Affected | Fixed in |
|---|---|---|
hono npm | All versions | 4.13.5 |
hono npm | All versions | 4.13.5 |
How do I fix CVE-2026-84363?
Upgrade hono to 4.13.5 or later.
Is CVE-2026-84363 being exploited?
There is no known exploitation of CVE-2026-84363 in the wild and no public exploit code.
Sources
Also known as CLEANSTART-2026-ZF21057, ECHO-5f0c-baeb-506a, GHSA-crvj-82cr-hjcx, MINI-3hcc-xhhv-r5fx, MINI-5w8w-rf6w-cpmc, MINI-g3qp-46mm-676v and 5 more.