A critical vulnerability in next-mdx-remote has been identified that allows attackers to execute arbitrary code on servers performing React server-side rendering (SSR). Tracked as CVE-2026-0969, this flaw poses a severe risk to applications that dynamically render untrusted MDX content, including blogs, documentation portals, and user-generated content platforms.
For CISOs, developers, and DevOps teams, this represents a pressing security concern: the attack can give malicious actors full control over the server environment, leading to data theft, malware installation, or complete server takeover.
In this article, we’ll explain how this vulnerability works, its technical mechanics, real-world risk, and actionable steps to secure your Next.js applications.
What Is Next-Mdx-Remote and MDX?
Next-Mdx-Remote is an open-source TypeScript library designed for Next.js applications. It allows developers to fetch MDX (Markdown with JSX) from external sources like databases, APIs, or user input, and render it dynamically on the server or client.
Why MDX Is Popular
- Combines Markdown simplicity with React components
- Enables rich, interactive content for blogs and documentation
- Supports dynamic rendering on server-side and client-side
However, this flexibility comes at a risk: when MDX includes user-supplied content, improper sanitization can allow malicious JavaScript to run in the server context.
How the Vulnerability Works (CVE-2026-0969)
The critical flaw lies in the serialize and compileMDX functions of versions 4.3.0 through 5.0.0 of next-mdx-remote.
Technical Mechanics
- Malicious MDX can include JavaScript expressions inside curly braces
{} - Examples:
eval(),Function(),require() - During server-side rendering, these expressions are executed with full server privileges, leading to remote code execution (RCE)
Example Attack:
{require('child_process').execSync('rm -rf /')}
If executed on a vulnerable server, this could delete files, exfiltrate data, or install malware.
Impact
| Aspect | Information |
|---|---|
| CVE ID | CVE-2026-0969 |
| Affected Versions | 4.3.0 – 5.0.0 |
| CVSS Score | Critical (9.8/10 estimated) |
| Impact | Arbitrary code execution via SSR on untrusted MDX |
Real-World Implications
Attackers targeting SSR platforms with untrusted MDX can:
- Steal sensitive server data (databases, API keys, secrets)
- Deploy ransomware or malware
- Gain persistent control over enterprise servers
- Exploit cloud-hosted Next.js apps in SaaS or PaaS environments
The vulnerability is particularly dangerous for multi-tenant platforms that accept user-generated MDX content.
Mitigation and Best Practices
1. Upgrade Immediately
- Next-mdx-remote 6.0.0 fixes the vulnerability
- Default setting blocks JavaScript expressions (
blockJS: true) - For advanced users:
blockJS: false+blockDangerousJS: trueensures risky globals (process, eval, require) are filtered
2. Never Render Untrusted MDX Directly
- Sanitize all user-supplied content
- Use libraries like remark-rehype for safe HTML and JSX conversion
3. Audit Server-Side Rendering Code
- Review all calls to
compileMDXandserialize - Ensure no unsafe JS evaluation occurs
4. Test in Staging
- Verify your application for breaking changes introduced by version 6.0.0
- Confirm that sanitized MDX renders correctly without enabling unsafe JS execution
Additional Security Measures
- Implement Web Application Firewall (WAF) rules for MDX endpoints
- Use static content generation for user content whenever possible
- Monitor server logs for suspicious runtime execution
- Integrate CI/CD security checks for dependencies and MDX libraries
Framework Alignment and Compliance
Following industry security standards helps mitigate risk:
- OWASP Secure Coding Guidelines
- NIST Application Security Controls
- ISO 27001 Control Objectives
Proper handling of untrusted MDX aligns with secure software development practices and regulatory compliance, reducing liability and risk exposure.
Expert Insight
Why this vulnerability is critical:
Next-mdx-remote’s flexibility is a double-edged sword. Without strict sanitization, SSR becomes an attack vector. Developers and security teams must treat all user-supplied MDX as untrusted input, similar to handling raw SQL or API data.
Risk takeaway:
Even a single unsanitized compileMDX call on a production server can result in full server compromise.
FAQs: Next-Mdx-Remote Vulnerability
What versions are affected by CVE-2026-0969?
Versions 4.3.0 through 5.0.0 of next-mdx-remote are vulnerable. Upgrade to 6.0.0 immediately.
How does the vulnerability enable RCE?
Malicious JavaScript expressions in untrusted MDX are executed during server-side rendering, giving attackers full control over the server.
Can this vulnerability affect client-side MDX rendering?
No. The RCE risk is specific to server-side rendering where the server executes JS expressions from MDX.
How can developers safely render user-generated MDX?
Sanitize all MDX content using tools like remark-rehype and block JavaScript expressions using blockJS: true.
Does upgrading to 6.0.0 break existing MDX code?
Yes, if your MDX relied on JavaScript expressions. Test in staging and adjust settings (blockJS, blockDangerousJS) carefully.
Conclusion
CVE-2026-0969 in next-mdx-remote highlights the critical need for secure server-side rendering practices in React applications. Organizations must:
- Upgrade immediately to version 6.0.0
- Sanitize all untrusted MDX content
- Audit compileMDX and serialize calls
- Apply secure coding and SSR best practices
Failure to act exposes servers to remote code execution, data theft, and malware deployment. Proactive mitigation ensures both compliance and operational security.
Next Step: Review your MDX rendering pipeline, implement sanitization, and run dependency vulnerability scans to prevent RCE attacks.
