CVE-2026-27977

What is this vulnerability?

CVE-2026-27977 is categorized as a critical Cross-Site Scripting (XSS) flaw. Based on our vulnerability intelligence, this issue occurs when the application fails to securely handle untrusted data boundaries.

Next.js is a React framework for building full-stack web applications. Starting in version 16.0.1 and prior to version 16.1.7, in next dev, cross-site pr...

This architectural defect enables adversaries to bypass intended security controls, directly manipulating the application's execution state or data layer. Immediate strategic intervention is required.

Risk Assessment

Impact on Systems

✅ Session Hijacking: Attackers can steal active user session tokens (cookies) to impersonate the victim.

✅ Phishing Execution: Malicious scripts can dynamically alter DOM content to present fraudulent login forms.

✅ Worm Propagation: Stored XSS can spread autonomously as users visit the infected page.

How to fix this issue?

Implement the following strategic mitigations immediately to eliminate the attack surface.

1. Output Encoding Implement strict context-aware output encoding (HTML, JavaScript, Attribute, CSS) before rendering user data.

2. Content Security Policy (CSP) Deploy a rigorous CSP header to restrict script execution exclusively to trusted domains.

3. Framework Defenses Utilize native UI framework protections (e.g., React DOM escaping) and avoid dangerouslySetInnerHTML.

Vulnerability Signature

// Example DOM-based XSS vulnerability
const user_input = new URLSearchParams(window.location.search).get('q');
// VULNERABLE: Direct insertion into innerHTML
document.getElementById('results').innerHTML = "Results for: " + user_input; 

// EXPLOIT PAYLOAD: ?q=\<img src=x onerror=alert(document.cookie)\>

References and Sources

• NVD — CVE-2026-27977
• MITRE — CVE-2026-27977
• CWE-1385 — MITRE CWE
• CWE-1385 Details
• PII and Secrets Exposure