CVE-2026-59896: Hono race condition in JSX server-side rendering context isolation

CVE-2026-59896 · Severity: medium · CVSS 6.5 · Published 2026-07-08

Hono is a web framework used to build fast applications. A flaw in its JSX component system could allow one user's private data to be accidentally shown to another user when the server is processing multiple requests at the same time. This could lead to unauthorized data exposure or incorrect security decisions if the system confuses which user is currently logged in.

Technologies: hono (npm). Vendors: npm.

Quick answers

Is CVE-2026-59896 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-59896 being exploited in the wild.
How severe is CVE-2026-59896?
Medium severity, with a CVSS score of 6.5, published 8 July 2026.
Which products and versions are affected?
hono (npm) >= 4.11.8, < 4.12.27, SEMVER:introduced=4.11.8,fixed=4.12.27.
Is there a fix for CVE-2026-59896?
Yes. hono (npm): upgrade to 4.12.27 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-59896 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-59896?
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 4.12.27 or later
    npm install hono@4.12.27

Technical details

A race condition exists in the hono/jsx component during server-side rendering (SSR) where context values are stored in a process-wide structure rather than being scoped to individual requests. When an asynchronous component suspends on an 'await' call, its context value remains observable and can be overwritten by concurrent requests. An attacker or concurrent user could trigger a state where useContext() returns data belonging to a different in-flight request. This vulnerability specifically affects async components where context is read after an await; synchronous rendering and client-side rendering are unaffected. The issue is fixed in version 4.12.27.

Affected products

  • honojs hono >= 4.11.8, < 4.12.27

Identifiers

  • CVE-2026-59896
  • GHSA-hvrm-45r6-mjfj

Timeline

  • 2026-06-23: disclosed: Vulnerability published to honojs/hono repository
  • 2026-06-23: patched: Version 4.12.27 released
  • 2026-07-08: advisory: NVD published CVE-2026-59896
  • 2026-07-21: advisory: GitHub Advisory GHSA-hvrm-45r6-mjfj reviewed and updated

References

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