CVE-2018-8373 is a memory corruption vulnerability in Microsoft Internet Explorer Scripting Engine. CISA added it to the Known Exploited Vulnerabilities catalogue on 25 March 2022, which means attackers have used it in real attacks. A remote code execution vulnerability exists in the way that the scripting engine handles objects in memory in Internet Explorer.
What This Vulnerability Means in Practice
CVE-2018-8373 is a memory corruption flaw in the Internet Explorer scripting engine, which matters because a parser or object-handling bug in a browser engine can be turned into code execution when a victim opens crafted web content.
For an attacker, the danger is not just the bug itself, but the fact that browser scripting engines run in a highly exposed execution path. A memory corruption condition in that path can become a reliable entry point for drive-by exploitation, especially when the target environment still allows legacy browser components to process untrusted content.
Why Memory Corruption in a Scripting Engine Is Dangerous
Memory corruption vulnerabilities are dangerous because they can break the boundary between data and code. In a scripting engine, that often means malformed objects, use-after-free style behaviour, or other unsafe memory state can be shaped into arbitrary execution if the attacker can control enough of the execution flow.
That risk is amplified in browser-facing components because the attacker does not need prior access to the endpoint. They only need a delivery path, such as a malicious page, injected content, or another web-delivered lure that causes the vulnerable code path to run.
When a browser engine is the affected product, the blast radius is often broader than a single application. Any legacy dependency on the affected browser technology can enlarge exposure across a fleet, which is why organisations should treat browser-engine defects as potentially high-impact even when the initial bug class looks narrow.
How Organisations Check Exposure and Prioritise Action
Exposure review should start with asset inventory, browser usage, and any remaining dependency on Internet Explorer scripting behaviour. Teams should verify whether the vulnerable component is present on managed endpoints, whether legacy web applications still require it, and whether the environment permits untrusted web content to reach those systems.
Public exploitability should also drive prioritisation. Because CISA added this CVE to the Known Exploited Vulnerabilities catalogue, the issue should be handled as a real exploitation concern rather than a theoretical one. For version and patch specifics, readers should use the CVE Program and the NIST National Vulnerability Database rather than relying on secondary summaries.
Vulnerability management should then confirm whether the affected software is internet-facing, reachable through common user workflows, or embedded in a business process that would make exploitation easier to trigger at scale.
Remediation, Detection, and Post-Exploitation Review
Remediation should follow the vendor advisory and CISA KEV guidance for the exact product version, but the broader control question is whether the organisation can remove the vulnerable execution path quickly enough. If patching is delayed, compensating controls may include reducing exposure to untrusted content, restricting legacy browser use, and hardening the systems that still depend on the affected component.
Detection should look for signs of malicious web activity, unusual browser-process crashes, script-engine anomalies, and suspicious child processes or follow-on execution after browsing activity. Memory corruption flaws are often used as the first step in a chain, so post-patch review should also search for persistence, dropped files, new services, and unusual authentication or session activity on the endpoint.
If exploitation is suspected, the investigation should extend beyond the browser itself. Compromise of a user session, browser credentials, or access tokens can turn a browser exploit into wider account abuse, especially where the endpoint is used for enterprise applications or remote administration.
Risk and Threat Considerations
This CVE carries direct exploitation risk because it is an externally reachable memory corruption bug in a widely used browser scripting engine. The main concern is that an attacker can use web content to trigger code execution on a victim system, then pivot from the browser into the broader endpoint environment.
Failure mechanism: Crafted content drives the scripting engine into unsafe memory handling, allowing the attacker to move from code execution to execution under the victim’s user context and, in some cases, a deeper compromise chain.
Impact: Successful exploitation can enable malware delivery, credential theft, session abuse, endpoint persistence, and downstream movement into internal resources that the browser session can reach.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
NIST SP 800-53 Rev 5 and CIS Controls v8 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-53 Rev 5 | SI-2 — Flaw Remediation | This CVE requires timely flaw remediation for exposed browser software. |
| SI-3 — Malicious Code Protection | Drive-by exploitation and follow-on payloads make endpoint malicious-code controls materially relevant. | |
| AU-6 — Audit Review, Analysis, and Reporting | Browser exploitation and post-compromise review depend on correlating endpoint activity and unusual execution. | |
| Recommendation — Prioritise SI-2 remediation for the affected browser component and verify closure in vulnerability tracking. Strengthen SI-3 filtering and monitoring on endpoints that can reach untrusted web content. Use AU-6 to review browser and endpoint logs for exploit traces and post-intrusion activity. | ||
| CIS Controls v8 | CIS-7 — Continuous Vulnerability Management | KEV-listed exploitation makes prioritised vulnerability management central to this CVE. |
| CIS-10 — Malware Defenses | Exploitation often leads to payload delivery or post-exploitation malware on the endpoint. | |
| Recommendation — Prioritise CIS-7 remediation for the KEV-listed browser flaw and validate exposure closure. Apply CIS-10 to detect and block payloads delivered after browser exploit execution. | ||
Practitioner Guidance
Why practitioners should care: Treat this class of browser-engine flaw as an exposure-management problem, not only a patching ticket. If Internet Explorer compatibility still exists in the environment, that legacy dependency can keep a known exploitation path alive long after the browser is no longer a primary user choice.
What to watch for: Prioritise hosts that still process untrusted web content through legacy browser components, especially endpoints used for high-value accounts or administrative workflows. When the vulnerable path is still enabled, risk persists even if the browser seems dormant.
Practitioner takeaway: The safest long-term fix is to remove reliance on the vulnerable browser path entirely, then confirm that the patch did not just close one exploit but left a usable legacy fallback behind.