Microsoft has taken swift action to tighten security around Internet Explorer (IE) mode in its Edge browser following credible intelligence that cybercriminals were exploiting it to compromise Windows environments.
The report, published by Microsoft’s Edge Security Team, reveals that attackers leveraged unpatched vulnerabilities in Internet Explorer’s JavaScript engine (Chakra) and abused in-browser features to execute code on victim devices, bypassing several layers of Chromium’s built-in protection mechanisms.
Exploiting Legacy Compatibility for Modern Attacks
The exploitation wave, detected in August 2025, stemmed from the intersection of legacy compatibility and modern browsing workflows.
Although the majority of the web has migrated to standards-compliant technologies, many enterprises still rely on outdated web stacks, especially internal systems built around ActiveX controls, Flash, or older camera interfaces.
For such cases, Edge maintains Internet Explorer mode to ensure critical operations remain functional during the process of modernization.
However, IE’s underlying design lacks the hardened, multi-process architecture and sandboxing techniques of Chromium.
According to Microsoft’s threat intelligence, attackers used a convincing spear-phishing or social engineering lure to direct targets to fake but “official-looking” corporate or government websites.
Once on-site, users were prompted to reload the page in IE mode via a deceptive pop-up, granting attackers the opportunity to invoke IE’s older JavaScript engine.
From there, an unpatched Chakra zero-day vulnerability allowed remote code execution, followed by a chained privilege-escalation exploit, providing complete system compromise.
The impact of such an attack extends far beyond initial access. Once administrative control is gained, threat actors could install persistence mechanisms, deploy info-stealing malware, or move laterally across connected corporate systems, posing a significant threat to enterprise networks.
Microsoft’s Mitigation and Long-Term Strategy
In response to these incidents, the Edge security team removed the most easily accessible entry points for reloading pages via IE mode, including the toolbar, the right-click context menu, and the main menu options.
IE mode functionality remains available for enterprise users through Microsoft’s existing policy framework, ensuring business continuity while hardening casual exploitation vectors.
For individual users requiring IE compatibility, the configuration process now demands manual activation through: Settings > Default Browser > Allow sites to be reloaded in Internet Explorer mode.
Users must then explicitly list compatible domains within the “IE mode pages” settings before reloading the site. Microsoft emphasizes that these extra steps are intended to introduce friction, making it significantly harder for attackers to automate or socially engineer the IE reload process.
Microsoft reiterated that Internet Explorer 11 officially reached end of life on June 15, 2022, and should only be used when absolutely necessary.
The company continues to recommend transitioning away from legacy code dependencies to benefit from modern Chromium-based security architecture, improved performance, and stricter content isolation.
By redesigning IE mode accessibility, Microsoft reinforces its ongoing balance between legacy compatibility and proactive defense, ensuring that businesses can transition safely without leaving open doors for cyberattacks.
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