In August 2025, Microsoft received credible reports indicating that unidentified threat actors were exploiting the Internet Explorer (IE) mode within its Edge browser to gain unauthorized access to user devices. This mode, designed to provide backward compatibility for legacy websites, became a vector for cyberattacks, prompting Microsoft to implement significant security enhancements.
Understanding the Exploitation Mechanism
The Microsoft Browser Vulnerability Research team detailed the attack methodology employed by these cybercriminals. Initially, users were deceived through social engineering tactics into visiting websites that appeared legitimate. Once on these sites, a flyout—a small overlay or pop-up—prompted users to reload the page using IE mode. This seemingly innocuous action was the first step in a sophisticated attack chain.
Upon reloading the page in IE mode, attackers exploited an unpatched vulnerability within Internet Explorer’s JavaScript engine, known as Chakra. This zero-day exploit allowed them to execute arbitrary code remotely on the victim’s device. The attack didn’t stop there; a subsequent exploit enabled the attackers to escalate their privileges beyond the browser environment, ultimately seizing full control of the compromised system.
Implications of the Attack
This exploitation method is particularly alarming because it circumvents the advanced security features integrated into modern browsers like Chromium and Microsoft Edge. By reverting to the less secure IE mode, attackers effectively bypassed these defenses, facilitating a range of malicious activities. These included deploying malware, moving laterally across networks, and exfiltrating sensitive data.
Microsoft’s Response and Security Enhancements
In response to these security breaches, Microsoft undertook a comprehensive overhaul of the IE mode’s accessibility within the Edge browser. The company removed several user interface elements that previously allowed for easy activation of IE mode, including:
– The dedicated toolbar button
– Context menu options
– Items within the browser’s hamburger menu
These changes aim to make the activation of IE mode a more deliberate process, thereby reducing the risk of inadvertent exploitation.
Guidelines for Enabling IE Mode
For users who still require IE mode for specific legacy applications or websites, Microsoft has outlined a more controlled activation process:
1. Access Browser Settings: Open the Edge browser and navigate to the ‘Settings’ menu.
2. Modify Default Browser Settings: Within the settings, select ‘Default Browser.’
3. Enable IE Mode: Locate the option labeled ‘Allow sites to be reloaded in Internet Explorer mode’ and set it to ‘Allow.’
4. Specify Sites for IE Mode: After enabling this setting, add the specific site(s) that require IE compatibility to the ‘Internet Explorer mode pages’ list.
5. Reload the Site: Navigate to the specified site, which will now load in IE mode.
By implementing these steps, users can ensure that the decision to use IE mode is intentional and limited to necessary instances, thereby mitigating potential security risks.
Balancing Security with Legacy Support
Microsoft acknowledges the delicate balance between maintaining security and providing support for legacy technologies. The company stated, This approach ensures that the decision to load web content using legacy technology is significantly more intentional. The additional steps required to add a site to a site list are a significant barrier for even the most determined attackers to overcome.
Historical Context and Ongoing Vigilance
This incident is not isolated; Internet Explorer has a history of vulnerabilities being exploited by malicious actors. For instance, in March 2025, Microsoft addressed 57 security flaws, including six zero-day vulnerabilities actively exploited in the wild. Among these was a use-after-free vulnerability in the Win32k driver, which allowed attackers to elevate privileges locally.
Similarly, in January 2020, Microsoft warned of an unpatched zero-day vulnerability in Internet Explorer that was under active attack. The flaw allowed attackers to execute arbitrary code in the context of the current user, posing significant risks, especially if the user had administrative rights.
These historical instances underscore the importance of continuous vigilance and prompt response to emerging threats. Microsoft’s proactive measures in enhancing the security of IE mode reflect a commitment to protecting users from evolving cyber threats.
Recommendations for Users
To further safeguard against potential exploits, users are advised to:
– Stay Updated: Regularly update the Edge browser and the operating system to ensure all security patches are applied promptly.
– Exercise Caution: Be wary of unsolicited prompts to reload pages in IE mode, especially from unfamiliar or untrusted websites.
– Limit IE Mode Usage: Use IE mode only when absolutely necessary for compatibility with specific legacy sites or applications.
– Implement Security Tools: Utilize reputable antivirus and anti-malware solutions to provide an additional layer of defense against potential threats.
By adhering to these recommendations and understanding the risks associated with legacy technologies, users can better protect themselves in the ever-evolving landscape of cybersecurity threats.
