CVE-2026-84364: Hono parseBody memory exhaustion with unbounded dot-notation nesting

CVE-2026-84364 · Severity: medium · CVSS 5.3 · Published 2026-09-01

Hono is a popular web framework for JavaScript used to build HTTP APIs and web applications. When dot-notation parsing is enabled in form field handling, an attacker can craft requests that cause excessive memory allocation, potentially crashing the server and causing service downtime. This affects only applications that explicitly enable dot-notation parsing, not the default configuration.

Technologies: hono (npm). Vendors: npm.

Quick answers

Is CVE-2026-84364 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-84364 being exploited in the wild.
How severe is CVE-2026-84364?
Medium severity, with a CVSS score of 5.3, 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-2026-84364?
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-2026-84364 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-84364?
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

The vulnerability exists in Hono's parseBody() method, which converts dot-separated form field names into nested JavaScript objects without enforcing limits on nesting depth or the total number of intermediate objects created. Each dot-separated segment in a field name creates an intermediate object, and empty segments are preserved, allowing a single field name to encode multiple nesting levels per byte. An attacker can exploit this through two attack patterns: a single deeply dotted field name or many shallowly dotted fields in one request body. Because the amplification occurs after the body has been accepted, normal request size limits do not prevent the attack. The vulnerability is triggered by sending concurrent requests to endpoints with dot-notation parsing enabled, exhausting the JavaScript heap and terminating the process. The issue was patched in version 4.13.5 by adding bounds on nesting depth and the number of objects created.

Affected products

  • Honojs Hono < 4.13.5

Identifiers

  • CVE-2026-84364
  • GHSA-g6gw-c38x-mqfc

Timeline

  • 2026-08-26: disclosed
  • 2026-09-08: patched: Version 4.13.5 released with fix
  • 2026-09-08: advisory: Published to GitHub Advisory Database

References

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