CVE-2026-59896: Hono Framework Context Isolation Vulnerability

CVE-2026-59896 Overview

CVE-2026-59896 is a race condition vulnerability [CWE-362] in Hono, a Web application framework for JavaScript runtimes. The flaw resides in the hono/jsx server-side rendering pipeline. Versions from 4.11.8 before 4.12.27 fail to isolate context values per request during asynchronous rendering. When an async component awaits, createContext, useContext, jsxRenderer, or useRequestContext data can leak from a concurrent in-flight request. The vulnerability is fixed in version 4.12.27.

Critical Impact
Attackers can trigger cross-request data leakage during concurrent server-side rendering, exposing session tokens, user identifiers, or other context-bound sensitive values to unauthorized requests.

Affected Products

Hono framework versions 4.11.8 through 4.12.26
Applications using hono/jsx server-side rendering with async components
Deployments relying on createContext, useContext, jsxRenderer, or useRequestContext

Discovery Timeline

2026-07-08 - CVE-2026-59896 published to the National Vulnerability Database
2026-07-08 - Last updated in NVD database

Technical Details for CVE-2026-59896

Vulnerability Analysis

Hono's JSX renderer stored context state in a module-level structure shared across all concurrent requests. During synchronous rendering, this design worked because a single request completed before the next one began accessing the context. Async components break that assumption. When an async component awaits a promise, the JavaScript event loop yields to other pending work, including rendering for another HTTP request. That second request overwrites the shared context, and when the first request resumes after the await, it reads the second request's values.

The consequence is a cross-request data leak. A user's page can render with another user's context, including any data injected via jsxRenderer middleware or useRequestContext. Exploitation does not require authentication and can occur under normal traffic when concurrent requests overlap.

Root Cause

The root cause is missing per-request context isolation in the hono/jsx renderer. The renderer used global mutable state rather than binding the context to the specific asynchronous execution flow. This constitutes a classic race condition between concurrent asynchronous renders sharing process-level state.

Attack Vector

An attacker sends concurrent HTTP requests to an endpoint that renders JSX with async components. When a target request awaits inside an async component, the attacker's request populates the shared context. The victim's continuation then reads attacker-influenced values, or the attacker receives the victim's context data in the response. The attack requires network access only and no user interaction.

typescript

// Patch excerpt: src/jsx/base.ts
 import { escapeToBuffer, resolveCallbackSync, stringBufferToString } from '../utils/html'
 import type { HtmlEscaped, HtmlEscapedString, StringBufferWithCallbacks } from '../utils/html'
 import { DOM_RENDERER, DOM_MEMO } from './constants'
+import {
+  captureRenderContext,
+  createContext,
+  globalContexts,
+  runWithRenderContext,
+  useContext,
+} from './context'
 import type { Context } from './context'
-import { createContext, globalContexts, useContext } from './context'
 import { domRenderers } from './intrinsic-element/common'
 import * as intrinsicElementTags from './intrinsic-element/components'
// Source: https://github.com/honojs/hono/commit/fab3b13639339cbd5ba1166a5b23d9ac30c5f64f

The patch introduces captureRenderContext and runWithRenderContext helpers that snapshot and restore the render context around each asynchronous boundary. This binds context state to the specific render invocation rather than a global variable.

typescript

// Patch excerpt: src/jsx/streaming.ts
 import { JSXNode } from './base'
 import { childrenToString } from './components'
 import { DOM_RENDERER, DOM_STASH } from './constants'
-import { createContext, useContext } from './context'
+import { captureRenderContext, createContext, useContext } from './context'
 import { Suspense as SuspenseDomRenderer } from './dom/components'
 import { buildDataStack } from './dom/render'
 import type { HasRenderToDom, NodeObject } from './dom/render'
// Source: https://github.com/honojs/hono/commit/fab3b13639339cbd5ba1166a5b23d9ac30c5f64f

Detection Methods for CVE-2026-59896

Indicators of Compromise

Rendered HTML responses containing user data that does not belong to the authenticated session
Application logs showing context values referenced under a user ID that differs from the request's authenticated identity
Support tickets reporting that users see another account's information in server-rendered pages
Deployed Hono versions between 4.11.8 and 4.12.26 in package-lock.json or yarn.lock

Detection Strategies

Inventory Node.js and edge runtime workloads and identify any dependency on hono within the vulnerable range
Add integration tests that fire concurrent requests with distinct context values and assert response isolation
Enable request correlation IDs in jsxRenderer output and diff them against the responding session

Monitoring Recommendations

Alert on responses where user-identifying markers embedded in the render context do not match the request's authenticated principal
Track anomaly spikes in concurrent async render duration during peak traffic windows
Monitor software composition analysis feeds for advisory GHSA-hvrm-45r6-mjfj

How to Mitigate CVE-2026-59896

Immediate Actions Required

Upgrade hono to version 4.12.27 or later across all environments
Audit application code for async JSX components that read useContext or useRequestContext after an await
Rotate any secrets or tokens that may have been exposed via cross-request context leakage during the vulnerable window

Patch Information

The fix is available in Hono v4.12.27. The remediation is tracked in GitHub Security Advisory GHSA-hvrm-45r6-mjfj and implemented in commit fab3b13. The patch wraps async render calls with runWithRenderContext to isolate context per request.

Workarounds

Refactor async JSX components to pass request-scoped data as props rather than through context when upgrading is not immediately possible
Serialize rendering by disabling concurrent request handling on affected routes until the patch is deployed
Move sensitive user data lookups outside of async render boundaries and inject them synchronously

bash

# Upgrade Hono to the patched release
npm install hono@^4.12.27

# Verify the installed version
npm ls hono