CVE-2026-93981: Hono JSX HTML Escaping XSS Vulnerability

CVE-2026-93981 Overview

CVE-2026-93981 is a Cross-Site Scripting (XSS) vulnerability in the Hono web framework affecting versions before 4.13.7. The flaw resides in hono/jsx server-side rendering paths, which fail to HTML-escape plain string values in specific rendering contexts. Attacker-controlled strings passed to Suspense, ErrorBoundary, Context.Provider, renderToString(), or renderToReadableStream() are treated as already-escaped markup. This allows injection of arbitrary HTML and script execution under the application's origin. The vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation.

Critical Impact
An attacker who controls string input rendered through the affected hono/jsx paths can execute arbitrary JavaScript in the victim's browser under the application's origin, enabling session theft and account takeover.

Affected Products

Hono framework versions before 4.13.7
Applications using hono/jsx for server-side rendering
Applications using hono/jsx/dom/serverrenderToString() or renderToReadableStream()

Discovery Timeline

2026-09-19 - CVE-2026-93981 published to NVD
2026-09-21 - Last updated in NVD database

Technical Details for CVE-2026-93981

Vulnerability Analysis

The vulnerability stems from inconsistent HTML escaping behavior in hono/jsx server-side rendering. Multiple rendering paths stringify their input and then treat the resulting string as pre-escaped HTML markup. This assumption breaks the contract that JSX children are safely escaped by default.

The affected paths include plain strings rendered as a child or fallback of Suspense, string children of ErrorBoundary alongside asynchronous siblings, single children of Context.Provider, and root values passed directly to renderToString() or renderToReadableStream() from hono/jsx/dom/server. In each case, the string bypasses the framework's escaping pipeline.

Root Cause

The root cause is a missing HTML entity encoding step in specialized rendering paths. Standard JSX rendering escapes text children automatically, converting characters like <, >, and & to entity references. The affected code paths omit this step because they assume the stringified input is already-safe markup. This violates the principle of safe-by-default output encoding for user-controlled data.

Attack Vector

Exploitation requires an application to render attacker-controlled string data through one of the vulnerable code paths during server-side rendering. An attacker submits input containing HTML tags or script payloads through any input surface that reaches an affected rendering context. When the server renders the response, the payload is written to the HTML document without encoding.

The injected markup executes in the victim's browser under the application's origin. This grants the attacker access to cookies, session tokens, and DOM state accessible to first-party JavaScript. Refer to the GitHub Security Advisory GHSA-hxh3-vqpv-xpqv and the VulnCheck Advisory on Hono XSS for additional technical detail.

Detection Methods for CVE-2026-93981

Indicators of Compromise

Server response bodies containing unencoded <script> tags or event handler attributes originating from user-submitted fields
Client-side console errors or Content Security Policy violation reports referencing unexpected inline script execution
Anomalous outbound requests from browser sessions to attacker-controlled domains following interaction with rendered content

Detection Strategies

Perform a dependency audit across Node.js projects to identify hono versions below 4.13.7 in package.json and lockfiles
Review server-side rendering code for use of Suspense, ErrorBoundary, Context.Provider, renderToString(), and renderToReadableStream() with user-controlled string inputs
Deploy Content Security Policy (CSP) with script-src restrictions and monitor report-uri endpoints for injection attempts

Monitoring Recommendations

Aggregate web application firewall (WAF) logs for common XSS payload patterns targeting endpoints backed by Hono applications
Enable browser telemetry through CSP reporting to identify blocked inline scripts on production origins
Track dependency versions in continuous integration pipelines and fail builds when vulnerable hono releases are detected

How to Mitigate CVE-2026-93981

Immediate Actions Required

Upgrade the hono package to version 4.13.7 or later across all affected applications
Audit server-rendered components that pass user-controlled strings through Suspense, ErrorBoundary, Context.Provider, or the hono/jsx/dom/server entry points
Deploy or tighten a Content Security Policy that blocks inline scripts to reduce impact of any residual injection

Patch Information

Hono version 4.13.7 corrects the escaping behavior in the affected rendering paths. Update the dependency in package.json and regenerate the lockfile. See the GitHub Security Advisory GHSA-hxh3-vqpv-xpqv for the authoritative patch reference.

Workarounds

Manually HTML-encode user-controlled string values before passing them to affected rendering contexts
Wrap string children in a JSX element (such as a <span>) rather than passing them directly as the single child of Context.Provider or as a Suspense fallback
Route sensitive rendering through explicit escaping utilities until the upgrade is deployed

bash

# Upgrade Hono to a fixed version
npm install hono@^4.13.7

# Verify the installed version
npm ls hono