Is CVE-2020-0878 (Microsoft Edge and Internet Explorer Memory Corruption) being exploited in the wild?

Yes. CISA added CVE-2020-0878 to its Known Exploited Vulnerabilities catalogue on 3 November 2021, which it does only when there is reliable evidence of active exploitation. CISA lists it as known to be used in ransomware campaigns. Microsoft Edge and Internet Explorer contain a memory corruption vulnerability that allows attackers to execute code in the context of the current user.

What makes this a true in-the-wild exploitation case?

CVE-2020-0878 is not just a theoretical browser flaw, it is the kind of issue security teams treat as active exposure once it appears in the KEV catalogue. That matters because browser memory corruption can become a reliable user-context code execution path, especially when an attacker can pair it with a lure, malicious content, or a chained exploit. Use the CISA Known Exploited Vulnerabilities Catalog to confirm the current remediation expectation.

A browser exploitation case also needs to be read as an endpoint and identity-adjacent risk, not only a software defect. If the browser session is already authenticated to internal services, the attacker may inherit the user’s active access, saved state, and reachable web applications. That is why a browser CVE can quickly become a foothold rather than a standalone crash issue.

What should you verify on affected endpoints?

First confirm where Microsoft Edge and Internet Explorer are present, enabled, or still callable through legacy compatibility paths. Then determine whether those systems are internet-facing, routinely used for untrusted browsing, or used by privileged staff whose browser session would expose more downstream access if compromised. The key question is not just whether the vulnerable software exists, but whether it can be reached in a realistic attack path.

You should also look for signs that a browser-based intrusion has already begun. Suspicious child processes, unusual downloads, new persistence entries, redirected browser traffic, and web sessions that behave as if they were controlled externally are all useful indicators. For browser exploitation, compromise review is most valuable when it includes both endpoint telemetry and web activity, because the initial exploit often leaves only brief visible evidence.

For vulnerability status and record hygiene, validate against the official CVE record in the CVE Program and corroborate exposure data through the NIST National Vulnerability Database.

How should you respond when patching is delayed?

If remediation cannot happen immediately, reduce the chance that the flaw can be triggered through routine browsing. The practical approach is to limit exposure to untrusted web content, harden browser settings, and remove unnecessary legacy browser use where possible. When a browser vulnerability is in KEV, compensating controls should be temporary and explicit, not a substitute for fixing the exposed systems.

If the vulnerable browser may have been used before remediation, treat credential and session review as part of the response. Review active sessions, sign-in tokens, and any privileged web applications reachable from the affected browser context. Where there is evidence of successful exploitation or suspicious post-exploitation activity, rotate affected credentials and invalidate sessions that may have been exposed through the browser context.

Risk and Threat Considerations

Browser memory corruption is attractive to attackers because it can turn normal user interaction into code execution without requiring administrative rights. Once that happens, the browser becomes a launch point for phishing follow-on activity, credential theft, lateral web access, or additional payload delivery, especially if the affected user is logged into business systems.

Failure mechanism: Exploitation succeeds when malicious content or a crafted page triggers memory corruption inside the browser engine, allowing code to run in the user’s security context and potentially extend into nearby web sessions or local user data.

Impact: The result can be account compromise, session hijacking, further malware delivery, or broader intrusion activity that starts from a single browser interaction and expands into enterprise access.

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-16 — Memory Protection	Browser memory corruption is a software integrity problem that maps to memory-protection controls.
	SI-2 — Flaw Remediation	The subject is an actively exploited vulnerability requiring remediation and validation.
	IR-4 — Incident Handling	Known exploitation requires compromise assessment and response actions after exposure.
Recommendation — Harden browser execution paths and reduce exploitable memory-corruption exposure. Prioritise remediation of the vulnerable browser and verify deployment quickly. Investigate affected endpoints for signs of exploitation and contain suspicious activity.
CIS Controls v8	CIS-7 — Continuous Vulnerability Management	KEV-listed exploitation makes vulnerability identification and remediation central.
	CIS-8 — Audit Log Management	Post-exploitation review depends on endpoint and browser telemetry evidence.
Recommendation — Track, prioritise and remediate the vulnerable browser as an actively exploited issue. Collect and review endpoint and browser logs for exploitation indicators.

Practitioner Guidance

What to prioritise: Treat endpoints that still run Internet Explorer or legacy Edge dependencies as higher priority than general desktop populations, especially if they belong to privileged users or staff with broad SaaS access. Those systems create the most valuable browser session for an attacker.

What to verify: Confirm not only whether the browser is installed, but whether it can still be launched in a way that exposes the vulnerable code path. Also verify whether telemetry can show browser crashes, unusual child processes, or suspicious network activity around the remediation window.

Decision rule: If you cannot patch immediately, reduce browser exposure first, then hunt for compromise indicators, then invalidate potentially exposed sessions or credentials. Do not wait for proof of abuse before containing the reachable attack surface.

Practitioner takeaway: For an exploited browser CVE, the operational question is not whether a patch exists, but whether the affected endpoints can still be used to turn one web interaction into usable access.