CVE-2019-0752

What is the IE Scripting Engine?

Internet Explorer's JScript/VBScript scripting engine parses and executes script embedded in web pages, translating attacker-supplied JavaScript into in-memory object operations. Because this engine processes untrusted content by design and manages complex object lifetimes, it has historically been one of the richest sources of exploitable memory-corruption bugs in Windows — type confusion and use-after-free flaws in scripting engines have powered a large share of drive-by browser exploit kits over the past decade.

Overview

CVE-2019-0752 is a High-severity remote code execution vulnerability caused by a type confusion (CWE-843) in the way Internet Explorer's scripting engine handles objects in memory. An attacker who convinced a victim to visit a specially crafted website — including via malicious ads or compromised legitimate sites — could execute arbitrary code with the same privileges as the current user. Microsoft fixed it in the April 2019 Patch Tuesday update, and CISA's KEV entry notes the flaw has also been used in ransomware operations.

Technical Details

A type confusion vulnerability occurs when code treats a memory object as one type while it actually holds a different, incompatible type — allowing an attacker to manipulate the resulting confusion to corrupt memory and hijack control flow. The attack requires the victim to open a malicious page or document (CVSS user interaction: Required, attack complexity: High) but no prior privileges, and once exploited grants full confidentiality, integrity, and availability impact through code execution in the user's context.

Discovery

Addressed through Microsoft's internal security review as part of its April 2019 Patch Tuesday cycle; no external researcher has been broadly credited for the original report.

Exploitation Context

CISA's KEV listing confirms this bug has been exploited in the wild and used in connection with ransomware intrusions. Scripting-engine memory-corruption bugs of this class were commonly bundled into commodity exploit kits and used in both broad drive-by campaigns and more targeted phishing operations delivering initial malware droppers, since many endpoints continued running legacy IE for internal line-of-business applications long after Edge became the default browser.

Remediation

1. Apply the April 2019 Patch Tuesday cumulative update (or any later update) for the affected Windows/IE version.
2. Migrate away from Internet Explorer wherever possible; where legacy IE-only applications remain, isolate them using IE Mode in Microsoft Edge rather than the standalone browser.
3. Deploy Attack Surface Reduction rules and Windows Defender Exploit Guard to blunt browser-based exploit chains.
4. Filter or sandbox outbound web traffic through a secure web gateway to catch known exploit-kit infrastructure.
5. Review endpoint logs for signs of drive-by compromise (unexpected child processes spawned from the browser) on systems patched late.