Analysis Summary

Microsoft has released a critical security update for its Edge browser, addressing four major remote code execution vulnerabilities—CVE-2025-21342, CVE-2025-21408, CVE-2025-21283, and CVE-2025-21279. These vulnerabilities, found in Microsoft Edge version 133.0.3065.51 (based on Chromium 133.0.6943.53/54), could allow attackers to execute remote code by tricking users into clicking specially crafted malicious links. The attack vector is network-based, with phishing emails and malicious websites being the primary means of exploitation. Although none of these vulnerabilities have been publicly disclosed or exploited in the wild, their potential severity makes immediate updates crucial.

Each of these vulnerabilities enables attackers to gain control over the browser’s renderer process, compromising user confidentiality, integrity, and availability. CVE-2025-21342 and CVE-2025-21283 pose a significant threat, allowing attackers to view and modify user data or crash browser tabs. CVE-2025-21408 follows a similar pattern but is rated as "Exploitation Unlikely." CVE-2025-21279, while also enabling remote code execution, has been assessed as "Exploitation Less Likely." Despite these categorizations, Microsoft strongly advises users to update their browsers as a precautionary measure.

To mitigate these threats, Microsoft Edge users should update to version 133.0.3065.51 immediately by navigating to Settings > About Microsoft Edge, where updates will be installed automatically if available. Organizations should also ensure employees update their browsers and remain alert to phishing attacks that could exploit these vulnerabilities. Since all four flaws require user interaction, training employees to recognize suspicious links can further reduce risk exposure.

While Microsoft has categorized exploitation likelihood as low, the risk remains significant, especially given the evolving nature of cyber threats. Updating the browser is a straightforward but essential step in maintaining security. The rapid deployment of security patches highlights the importance of staying current with updates to protect against emerging vulnerabilities. Users and enterprises alike must prioritize security hygiene, ensuring their systems remain safeguarded against potential cyberattacks.

Impact

•  Remote Code Execution

Indicators of Compromise

CVE

• CVE-2025-21342

• CVE-2025-21408

• CVE-2025-21283

• CVE-2025-21279

Affected Vendors

Remediation

• Use Microsoft Automatic Update to apply the appropriate patch for your system, or the Microsoft Security Update Guide to search for available patches.
• Open Microsoft Edge and navigate to Settings > About Microsoft Edge to check for and install the latest update (version 133.0.3065.51).
• Avoid clicking on suspicious links in emails, messages, or websites, as these vulnerabilities require user interaction for exploitation.
• Deploy antivirus and endpoint security solutions that can detect and block malicious activity linked to exploit attempts.
• Implement web filtering and email security solutions to block access to known phishing sites and malicious attachments.
• Use SIEM solutions to track and analyze unusual browser behavior that could indicate an attempted exploit.
• Configure browser security settings to restrict JavaScript execution and sandbox untrusted content to reduce exposure.
• IT teams should enforce browser updates across all endpoints to ensure company-wide protection against these vulnerabilities.