Is CVE-2016-3351 (Microsoft Internet Explorer and Edge Information Disclosure) being exploited in the wild?

Yes. CISA added CVE-2016-3351 to its Known Exploited Vulnerabilities catalogue on 24 May 2022, which it does only when there is reliable evidence of active exploitation. CISA lists it as known to be used in ransomware campaigns. An information disclosure vulnerability exists in the way that certain functions in Internet Explorer and Edge handle objects in memory.

What “being exploited in the wild” means for this CVE

For this vulnerability, the practical question is not whether the flaw exists, but whether it has crossed from theoretical risk into active abuse. CISA’s KEV listing is the key signal that defenders should treat it as a real exposure, not a watchlist item. For browser flaws, that usually means exposure can exist simply through normal web use, without a user knowingly doing anything unusual.

That matters because information disclosure issues often support a larger attack chain. Even when the flaw does not directly yield code execution, leaked memory contents, object state, or security-relevant data can help an attacker reduce uncertainty, steer follow-on exploitation, or support post-compromise discovery of sensitive material.

How to confirm exposure and operational relevance

The first step is to establish whether the vulnerable browser family is still present anywhere in the environment, including unmanaged endpoints and legacy systems. For a browser CVE, asset inventory matters more than assumptions about default browser usage, because outdated installations often survive in long-tail desktops, virtual environments, kiosk systems, and application compatibility setups.

Defenders should then verify whether the affected browser is still reachable in normal workflows and whether compensating controls are in place. Current guidance suggests prioritising systems that still browse the open web, render untrusted content, or retain legacy compatibility settings, because those are the most realistic exposure paths for exploitation.

Use the CISA Known Exploited Vulnerabilities Catalog to confirm the operational status of the issue, and check the NIST National Vulnerability Database and the CVE Program for authoritative record context.

What to do if patching is delayed

If you cannot patch immediately, reduce exposure by limiting where the browser is used, tightening web access policy, and removing unnecessary legacy browser dependencies. For organisations that still rely on legacy IE or Edge compatibility modes, the risk is rarely the browser alone, it is the combination of legacy rendering paths, broad user access, and weak segregation between trusted and untrusted content.

Temporary containment should focus on shrinking the number of systems that can trigger the flaw and shrinking the value of any data that could be exposed if exploitation succeeds. That means restricting high-risk browsing, segmenting sensitive workloads from general-purpose browsing, and ensuring vulnerable endpoints are not the ones that hold the most sensitive sessions or credentials.

If you need a broader response playbook for active exploitation, Zero-Day and Exploited Vulnerabilities Guide is useful for triage and emergency mitigation, while Vulnerability Management Guide covers prioritisation, exceptions, and verification.

Risk and Threat Considerations

A KEV-listed browser information disclosure flaw is dangerous because the attacker often needs little more than a reachable endpoint and a browsing path. The immediate concern is not only disclosure itself, but whether the leaked material can help an attacker identify memory layout, session state, or adjacent secrets that make later compromise easier.

Failure mechanism: The browser processes attacker-influenced content or objects in a way that reveals data that should have remained isolated, and that disclosure can be chained into reconnaissance, privilege gain, or broader exploitation.

Impact: Organisations can face sensitive data exposure, increased likelihood of follow-on compromise, and greater confidence for an attacker already operating inside the environment or targeting it through web delivery.

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, CIS Controls v8 and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.

Framework	Control / Reference	Relevance
NIST SP 800-53 Rev 5	SI-2 — Flaw Remediation	Active exploitation makes prompt remediation of the browser flaw material.
	RA-5 — Vulnerability Monitoring and Scanning	Confirming exposure requires locating vulnerable browser instances across the estate.
Recommendation — Prioritise remediation of the exploited browser vulnerability and track exceptions to closure. Scan for affected browser installations and validate exposure against asset inventory.
CIS Controls v8	CIS-7 — Continuous Vulnerability Management	KEV-listed exploitation requires prioritised vulnerability handling and verification.
Recommendation — Prioritise and verify remediation for vulnerabilities known to be exploited.
NIST CSF 2.0	ID.RA-01 — Asset vulnerabilities are identified and documented	The question depends on confirming whether vulnerable browsers still exist.
	PR.PS-04 — Software is managed to meet cybersecurity objectives	Browser patching and legacy path reduction are part of managing software securely.
Recommendation — Identify and document affected browser assets before deciding response priority. Update or constrain the browser software path that enables exploitation.

Practitioner Guidance

What to verify: Confirm where the affected browser still exists, whether it is reachable from untrusted web traffic, and whether any legacy compatibility setting keeps the vulnerable code path alive. If you cannot prove those three things, treat the exposure as still active.

Escalation / exception: If the browser is used on systems that access sensitive portals, administrative interfaces, or internal applications, escalate the issue as an active vulnerability-management priority rather than a routine browser update. For a KEV-listed issue, delay should be an exception with a clear owner and deadline.

Practitioner takeaway: For a KEV-listed browser flaw, the deciding factor is not whether exploitation is technically possible, but whether the vulnerable code path is still reachable in your environment and whether any exposed data would materially help an attacker.