Summary
Astro: Reflected/Stored XSS via unescaped <script>/<style> tag content in JSX/MDX rendering
Astro's JSX and MDX rendering pipeline treated string children of <script> and <style> elements as trusted HTML. When a dynamic value was passed through a JSX expression, such as <script>{value}</script>, an attacker-controlled value containing </script> or </style> could terminate the element and inject arbitrary HTML and JavaScript.
Other JSX expression contexts escaped dynamic strings automatically. This behavior was limited to <script> and <style> children rendered through Astro's astro:jsx renderer, including MDX components.
Details
The affected rendering paths marked all string children of <script> and <style> elements as safe HTML, without distinguishing literal content generated by the compiler from dynamic expression values. An application was vulnerable when attacker-controlled data, such as a query parameter or CMS field, was interpolated directly into one of these elements.
For example, a value containing </script><script>alert(1)</script> passed to <script>{value}</script> was emitted without escaping. The browser interpreted the first closing tag as markup and executed the injected script.
The fix preserves raw rendering for literal script and style content while escaping dynamic string children like other JSX expression values.
Workarounds
Do not interpolate untrusted dynamic values directly into <script> or <style> element children. Applications that cannot upgrade should validate and contextually encode these values before rendering them.
Credit
Reported by @RKasai127.
Impact
Affected applications could be vulnerable to reflected or stored cross-site scripting. Exploitation required an application to pass attacker-controlled data directly as a dynamic child of a <script> or <style> element in MDX or through the astro:jsx runtime. Successful exploitation allowed arbitrary JavaScript execution in the victim's browser under the application's origin.
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
CVE-2026-114128 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and user interaction required. 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 (7.3.2); 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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This issue is patched in [email protected].
Frequently Asked Questions
- What is CVE-2026-114128? CVE-2026-114128 is a medium-severity cross-site scripting (XSS) vulnerability in astro (npm), affecting versions < 7.3.2. It is fixed in 7.3.2. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2026-114128? CVE-2026-114128 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 astro are affected by CVE-2026-114128? astro (npm) versions < 7.3.2 is affected.
- Is there a fix for CVE-2026-114128? Yes. CVE-2026-114128 is fixed in 7.3.2. Upgrade to this version or later.
- Is CVE-2026-114128 exploitable, and should I be worried? Whether CVE-2026-114128 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-2026-114128 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-2026-114128? Upgrade
astroto 7.3.2 or later.