Internet Explorer WebBrowser Control Abuse Lets Attackers Convert Clicks Into RCE

Internet Explorer’s legacy WebBrowser control can be abused to turn seemingly harmless user clicks into full remote code execution (RCE), even on systems that no longer use Internet Explorer as a standalone browser.

Although Microsoft officially ended support for IE, the Trident engine and WebBrowser ActiveX control remain embedded in numerous Windows applications built with Visual Basic, .NET, and C, providing attackers with a surprisingly powerful attack surface for converting basic user interaction into code execution.

Internet Explorer WebBrowser Control Abuse

Despite IE’s deprecation, the WebBrowser control is still treated as a first-class citizen in Windows’ security zone model, inheriting elevated permissions when hosted under special origins such as http://localhost or file: URLs.

In practice, this means that desktop applications exposing embedded browsers on localhost, email clients, Electron-based software, dev stacks like XAMPP, or bundled web consoles, may silently inherit IE’s quirks and high-privilege behaviors without any explicit opt-in from developers. Attackers can chain these behaviors to pivot from a benign-looking website to local file execution paths.

The underlying issue starts with how IE’s zone model prioritizes trust for resources based on origin. While regular websites are restricted to “safe” ActiveX components, pages served from localhost can access additional COM objects, access remote SMB shares, and open local files, creating a hierarchy in which file: and localhost contexts enjoy significantly more privileges than the public internet.

Researchers from Swarm PT Security found that by leveraging cross-site scripting (XSS) in a localhost-exposed app, it is possible to open local HTML files through IE’s WebBrowser control, effectively creating a “portal” from a remote attacker-controlled page into the victim’s local filesystem.

One notable chain begins with an attacker-controlled site exploiting XSS in a localhost web application that renders inside a WebBrowser control.

The malicious JavaScript then opens Microsoft Edge via the microsoft-edge: URL scheme, instructing Chromium-based Edge to download a crafted HTML payload directly into the victim’s Downloads folder without prompting the user.

When downloaded via localhost, this file is written without the Mark-of-the-Web (MOTW) alternate data stream, meaning Windows no longer applies the standard “file from the internet” protections and will not show additional prompts when scripts or dangerous COM objects execute from that file.

Once the payload lands without MOTW, the WebBrowser control can be redirected from the original localhost XSS to the freshly downloaded HTML. At this stage, the malicious page executes in a privileged local context. It can instantiate insecure COM components such as WScript.Shell is historically used to spawn processes like calc.exe.

IE’s legacy ActiveX security prompt remains the final visible barrier to full compromise. However, the attack now requires only a small amount of social engineering: the victim must click “Yes” on the ActiveX warning dialog, effectively granting the page authority to execute arbitrary commands.

Researchers also demonstrated that IE’s support for rich file types and embedded viewers further widens the exploitability window. For example, playlist formats such as .wax, .wmx, or .m3u can be opened through Windows Media Player ActiveX objects. When those playlists reference SMB paths, they can silently leak NTLM hashes during playback.

Other formats, such as XAML, ClickOnce .application, and VSTO .vsto plug-ins, introduce additional paths for code execution within the .NET or Office ecosystems, often gated only by lightweight prompts that attackers can wrap in convincing lures.

The most alarming aspect is how attackers can weaponize clickjacking on top of these primitives. By rendering local folders, SMB shares, or ZIP archives inside a tiny, invisible iframe that tracks the user’s cursor, adversaries can ensure that any double-click on the page actually targets a file listing inside the WebBrowser control.

In proof-of-concept exploits, the iframe points to a ZIP archive containing a malicious executable; when the victim double-clicks “anywhere” on the page, that click launches the file inside the embedded Explorer-like view with no MOTW-based warning and no clear indication that a local object is being executed.

Variants of the same technique also exploit drag-and-drop behavior inside the WebBrowser control. When a victim drags a file onto a specially crafted .lnk shortcut or .desklink file rendered via iframe, Windows may execute the shortcut’s target without enforcing MOTW checks, enabling RCE without any traditional security dialogs.

In some chains, the attacker arranges for malicious shortcuts to be dropped onto the victim’s desktop with trusted-looking icons, such as “This PC” or “Photos”, so that a later double-click completes the compromise in a way that appears entirely routine.

For defenders, the research underscores that “dead” components like IE can still create living risk when embedded in modern applications. Organizations should inventory software using the WebBrowser control and restrict or disable high-risk ActiveX CLSIDs, such as WScript.Shell, and avoid exposing localhost web interfaces that rely on IE for rendering.

Until such legacy dependencies are removed, attackers will continue to abuse seemingly benign clicks in IE’s WebBrowser control and convert them into reliable, low-friction RCE chains.

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