CVE-2026-84363: Hono query parser fragment interpretation differential

CVE-2026-84363 · Severity: medium · CVSS 5.9 · Published 2026-09-01

Hono's web framework incorrectly processes URL query parameters that appear after a hash fragment (#), allowing applications to read parameters that security proxies, WAFs, and logging systems cannot see. This causes cached responses to be served with incomplete cache keys and can lead to stored XSS vulnerabilities when parameters are reflected without escaping.

Technologies: hono (npm). Vendors: npm.

Quick answers

Is CVE-2026-84363 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-84363 being exploited in the wild.
How severe is CVE-2026-84363?
Medium severity, with a CVSS score of 5.9, published 1 September 2026.
Which products and versions are affected?
hono (npm) < 4.13.5, SEMVER:introduced=0,fixed=4.13.5.
Is there a fix for CVE-2026-84363?
Yes. hono (npm): upgrade to 4.13.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-84363 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-84363?
Check whether you run hono (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • hono (npm): upgrade to 4.13.5 or later
    npm install hono@4.13.5

Technical details

Hono's query parsing implementation does not follow standard URL semantics: it processes query parameters (introduced by ?) that appear after the URL fragment (#), whereas all standard URL consumers (browsers, new URL(), reverse proxies) correctly discard everything after the first #. The vulnerability is rooted in Hono's query helpers not aligning with its routing layer. Attack preconditions require the runtime to pass literal # characters to the application (affected runtimes include Node.js; Cloudflare Workers normalize fragments and are unaffected). An attacker can craft URLs like `/page#?admin=true` to inject parameters invisible to upstream WAFs, access control filters, and audit logging. In cached deployments, responses influenced by these hidden parameters are stored under cache keys that do not reflect them, leading to cache poisoning and potential XSS when parameters are reflected without escaping. The fix was released in version 4.13.5.

Affected products

  • Hono hono < 4.13.5

Identifiers

  • CVE-2026-84363
  • GHSA-crvj-82cr-hjcx

Timeline

  • 2026-08-26: disclosed
  • 2026-08-26: patched: Version 4.13.5 released
  • 2026-09-08: advisory

References

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