Missing Cross-Origin-Opener-Policy

Description

The Cross-Origin-Opener-Policy (COOP) header is designed to isolate browsing contexts and protect against cross-window attacks. Without COOP in place, an attacker can leverage shared references between the main window and newly opened tabs or pop-ups to manipulate or access sensitive information. This lack of isolation can lead to data leakage, clickjacking, or even timing-based exploits that require a less restricted browsing context. In some scenarios, attackers might hijack references to alter the parent or child window’s location, potentially injecting malicious content or redirecting users to harmful sites. Overall, the absence of a proper COOP configuration weakens the security boundaries between your site and external or malicious domains.

Remediation

Configure a Cross-Origin-Opener-Policy header (e.g., 'same-origin' or 'same-origin-allow-popups') within your server or application settings. Ensure all pages that open or are opened by other windows or frames comply with a consistent COOP policy to maintain a secure browsing context. If necessary, employ a Web Application Firewall (WAF) or network-level rules to detect and block suspicious cross-window interactions. Regularly review your COOP configurations, especially if your application relies on third-party scripts or iframes that might conflict with isolation requirements. This approach helps preserve integrity and reduces the risk of cross-window attacks or data leakage.

References

Severity

Owasp

Code: A05:2021

Category: Security Misconfiguration

Classification