Microsoft Edge has identified and mitigated a critical threat exploiting its Internet Explorer (IE) compatibility mode, closing off high-risk entry points and reinforcing security for both individual and enterprise users.
Although the web has largely embraced modern standards, many enterprise and government applications continue to rely on legacy technologies such as ActiveX controls and Flash.
To bridge this gap, Microsoft Edge offers IE mode, enabling users to access these older sites without leaving the comfort of a Chromium-based browser.
By designating specific domains to open in IE mode, organizations can maintain compatibility for essential business portals—and then seamlessly switch back to Edge’s secure browsing environment.
However, Internet Explorer was created before today’s stringent defense-in-depth practices and sandbox architectures. Its JavaScript engine, Chakra, lacks many of the mitigations now standard in modern browsers.
When Edge invokes IE mode, it temporarily returns to this older execution environment, which can expose users to vulnerabilities no longer present in Edge’s native rendering engine.
The Exploit: Chakra and Entry Point Abuse
In August 2025, intelligence obtained by the Edge security team revealed that malicious actors were targeting IE mode to bypass Chrome-style safeguards.
Their attack chain began with a spoofed, official-looking website designed to trick victims into believing they needed IE mode for full functionality. A deceptive flyout prompted users to reload the page in IE mode—effectively handing control over to Chakra.
Once the page reloaded, attackers deployed an undisclosed zero-day exploit against Chakra, achieving remote code execution within the browser process.
With a foothold established, they carried out a second exploit to escape the browser sandbox and elevate privileges to SYSTEM level.
At this point, threat actors could install malware, move laterally across networks, and exfiltrate sensitive data, all while appearing to navigate a legitimate legacy site.
The combination of social engineering and high-impact 0-day vulnerabilities made this vector especially dangerous, as it circumvented many of Edge’s Chromium-based security features.
Upon verifying active exploitation attempts and assessing the severity, the Edge browser security team removed the most accessible IE mode triggers.
The toolbar button, context-menu option, and hamburger-menu entries for “Reload in Internet Explorer mode” were immediately disabled for non-commercial users. No changes were made to enterprise policy controls; administrators can still enable IE mode for large-scale deployments via group policy or Microsoft Intune.
For individual users who genuinely require IE compatibility, IE mode remains available but now requires explicit configuration:
- Open Edge and navigate to Settings > Default Browser.
- Under Allow sites to be reloaded in Internet Explorer mode, select Allow.
- Add required URLs to the Internet Explorer mode pages list.
- Reload the page, which will now open in IE mode.
These additional steps ensure that loading legacy content is a deliberate, auditable action rather than a single click—raising the bar for attackers seeking to exploit IE’s vulnerabilities.
I Use IE Mode—What Should I Do?
Internet Explorer 11 reached its end of life on June 15, 2022, and no longer receives feature updates outside of critical security patches delivered through Edge.
Microsoft advises all users and organizations to migrate away from legacy web technologies as swiftly as possible. To verify or disable IE mode on your device, open Edge and go to Settings > Default Browser, then confirm your preferred compatibility setting.
By restricting casual access to IE mode and preserving enterprise policy controls, Microsoft Edge strikes a balance between legacy support and modern security.
These measures significantly reduce the attack surface associated with Internet Explorer’s outdated architecture while still accommodating genuine business needs.
Users and administrators are encouraged to review their IE mode configurations and transition to contemporary web standards wherever feasible, ensuring the highest levels of protection in today’s evolving threat landscape.
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