Summary
hono/jsx does not isolate context per request, leading to cross-request data disclosure
hono/jsx did not isolate context values per request during server-side rendering. While an async component was suspended on await, its provided context value stayed observable to other requests rendering concurrently, so useContext() could return a value from a different in-flight request.
Details
During server-side rendering, context values were kept in a process-wide structure rather than scoped to each request's render. While an async component awaited, another request entering the same provider could observe or replace the value; when the first render resumed, it could read the other request's context.
This affects the usual ways request-scoped data is passed through a server-rendered JSX tree:
createContext()/useContext()- the
jsxRenderermiddleware anduseRequestContext()
It arises only when context is read after an await inside an async component while requests render concurrently. Reading context synchronously (before any await), purely synchronous rendering, and client-side (DOM) rendering are not affected.
Impact
Under concurrent requests, a response could be rendered with another request's context. A user may receive HTML rendered for a different user, and an authorization check performed after an await may be evaluated against another user's data.
This may lead to:
- disclosure of rendered output intended for another user
- authorization decisions made with the wrong request's context
- cross-request mixing of session or other request-scoped state
Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing. Typical impact: TOCTOU exploits, data corruption, or privilege escalation.
CVE-2026-59896 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.12.27); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-59896? CVE-2026-59896 is a medium-severity race condition vulnerability in hono (npm), affecting versions >= 4.11.8, < 4.12.27. It is fixed in 4.12.27. Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing.
- How severe is CVE-2026-59896? CVE-2026-59896 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of hono are affected by CVE-2026-59896? hono (npm) versions >= 4.11.8, < 4.12.27 is affected.
- Is there a fix for CVE-2026-59896? Yes. CVE-2026-59896 is fixed in 4.12.27. Upgrade to this version or later.
- Is CVE-2026-59896 exploitable, and should I be worried? Whether CVE-2026-59896 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-59896 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-59896? Upgrade
honoto 4.12.27 or later.