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CVE-2026-71850: CVE-2026-71850: Server-Side Rendering Data Exposure in Hono JSX Memoization

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CVE-2026-71850: Server-Side Rendering Data Exposure in Hono JSX Memoization

Vulnerability ID: CVE-2026-71850
CVSS Score: 4.8
Published: 2026-08-07

A session data exposure vulnerability in the Hono web application framework (hono/jsx module) allows consecutive users to receive cached HTML outputs containing private data. When JSX components wrapped in memo() are rendered on the server, the caching mechanism utilizes a module-level closure that persists across independent HTTP requests. When subsequent requests occur with matching props, the components are not re-evaluated, and cached HTML is served. If these components read request-scoped or session-specific data via ambient APIs, the data of the first user is exposed to subsequent users.

TL;DR

A session isolation flaw in Hono's JSX SSR engine caches rendered HTML globally when using the memo() utility. This causes the framework to serve cached data (including CSRF tokens and user profile details) belonging to previous users to subsequent visitors when components are rendered with identical props.

⚠️ Exploit Status: POC

Technical Details

  • CWE ID: CWE-488 (Exposure of Data Element to Wrong Session)
  • Attack Vector: Network
  • CVSS Score: 4.8 (Medium)
  • EPSS Score: N/A
  • Exploit Status: Proof-of-Concept
  • Affected Versions: >= 3.8.0, < 4.12.34
  • Impact: Information Disclosure (Request-scoped data, CSRF tokens)

Affected Systems

  • Hono applications using server-side rendering (SSR) with hono/jsx

Mitigation Strategies

  • Upgrade the hono package to version 4.12.34 or higher.
  • Remove the memo() wrapper from server-side rendered components.
  • Refactor components to accept all dynamic, request-scoped parameters as props rather than reading ambient context values.

Remediation Steps:

  1. Verify current Hono framework version using npm list hono or yarn licenses list.
  2. Update Hono to version 4.12.34 or higher: npm install hono@4.12.34.
  3. Audit codebase for the import and usage of memo from 'hono/jsx' or 'hono/jsx/dom'.
  4. Remove memo() wrappers around server-side components that retrieve request-specific information.
  5. Deploy the patched application to production and monitor server access logs.

References

Read the full report for CVE-2026-71850 on our website for more details including interactive diagrams and full exploit analysis.

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