honojs Hono up to 4.13.4 Cache Middleware cross site scripting

Summaryinfo

A vulnerability categorized as problematic has been discovered in honojs Hono up to 4.13.4. This affects an unknown part of the component Cache Middleware. Such manipulation leads to cross site scripting. This vulnerability is documented as CVE-2026-84363. The attack can be executed remotely. There is not any exploit available.

Detailsinfo

A vulnerability was found in honojs Hono up to 4.13.4. It has been rated as problematic. Affected by this issue is an unknown functionality of the component Cache Middleware. The manipulation with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Impacted is integrity. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-84363 since 09/01/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Successful exploitation requires user interaction by the victim. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1059.007.

Upgrading to version 4.13.5 eliminates this vulnerability.

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Productinfo

Vendor

• honojs

Name

• Hono

Version

• 4.13.0
• 4.13.1
• 4.13.2
• 4.13.3
• 4.13.4

Website

• Product: https://github.com/honojs/hono/

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