CVE-2018-8298

What is ChakraCore?

ChakraCore is the open-source JavaScript engine that powered Microsoft Edge (the original EdgeHTML-based browser) before Edge migrated to Chromium. As with any JavaScript engine, ChakraCore must safely manage a huge variety of dynamically-typed object shapes and just-in-time compiled code paths, and subtle mistakes in how it tracks an object's type can lead to serious memory-safety bugs reachable simply by visiting a malicious webpage.

Overview

CVE-2018-8298 is a type confusion vulnerability in the ChakraCore scripting engine that can lead to remote code execution. An attacker who convinces a victim to visit a specially crafted webpage (or view attacker-controlled content that invokes the engine) can trigger the engine to treat one object type as another, corrupting memory in a way that can be leveraged into arbitrary code execution in the context of the browser process.

Technical Details

The root cause is CWE-843 (Type Confusion): JavaScript engines like ChakraCore optimize object property access using internal type/shape tracking, and if the engine's assumptions about an object's runtime type can be invalidated by attacker-controlled script (for example, through crafted prototype manipulation or specific sequences of property additions), later code may read or write memory using the wrong type's layout, corrupting adjacent data or object metadata. This is a well-known and historically fruitful bug class across all major JavaScript engines. Exploitation requires user interaction (visiting a malicious page) but no authentication.

Discovery

The vulnerability was addressed through Microsoft's regular security update process, credited to security researchers who reported it through Microsoft's coordinated disclosure program.

Exploitation Context

CISA added CVE-2018-8298 to the KEV catalog in March 2022 based on confirmed exploitation. Browser scripting-engine vulnerabilities like this one are a recurring target for both criminal drive-by download campaigns and more targeted watering-hole style attacks, since a single malicious or compromised webpage can compromise any visiting victim without further interaction.

Remediation

1. Apply the July 2018 Windows/Edge security update (or later cumulative update) addressing CVE-2018-8298.
2. Migrate to the modern Chromium-based Microsoft Edge if any legacy EdgeHTML/ChakraCore-based browser is still in use, as it is no longer maintained.
3. Keep browser and OS auto-update mechanisms enabled to ensure timely delivery of future scripting-engine patches.
4. Deploy browser exploit mitigations (e.g., Windows Defender Exploit Guard / Attack Surface Reduction rules) to raise the cost of exploiting memory-corruption bugs even before patching.
5. Monitor endpoint telemetry for anomalous browser process behavior, such as unexpected child process creation, which can indicate successful browser exploitation.