Is CVE-2013-3893 (Microsoft Internet Explorer Resource Management Errors) being exploited in the wild?

Yes. CISA added CVE-2013-3893 to its Known Exploited Vulnerabilities catalogue on 12 August 2025, which it does only when there is reliable evidence of active exploitation. CISA has not linked it to known ransomware campaigns. Microsoft Internet Explorer contains a memory corruption vulnerability that allows for remote code execution. Any organisation running the affected product should treat remediation as urgent.

How to interpret active exploitation for CVE-2013-3893

The practical meaning of “being exploited in the wild” is that you should treat this as an active threat, not a theoretical vulnerability. The question is not whether the bug exists, but whether exposed Internet Explorer installations still present an exploitable path that attackers can use for remote code execution and initial foothold.

For teams still carrying legacy browser exposure, the first task is to confirm where Microsoft Internet Explorer remains enabled, reachable, or embedded in legacy workflows. That includes shared workstations, unmanaged desktops, long-tail virtual machines, and systems where compatibility settings keep the browser available even if staff do not use it day to day.

For broader vulnerability handling, align the response with a formal prioritisation workflow such as Vulnerability Management Guide, because exploited vulnerabilities need verification, scope, and an explicit remediation owner rather than informal ticketing. If your organisation treats browser exposure as part of endpoint hardening, the Enterprise Browser and Browser Security Guide is also relevant to reducing the attack surface around legacy browser use.

What remediation should happen first

The immediate priority is to remove or neutralise the vulnerable browser where that is operationally possible, then verify that the environment no longer allows the affected code path to be used. When a vulnerability is known to be actively exploited, the correct sequence is exposure reduction first, then validation, then longer-term hardening.

If patching is available, it should be treated as urgent and tracked to completion on every in-scope asset, not only the obvious user endpoints. If patch deployment must wait because of business dependency or compatibility testing, compensate with temporary controls that reduce exploitability, such as removing access to the browser, blocking high-risk execution paths, or isolating users who must still open legacy content.

For exploit-driven remediation, the broader lesson from Zero-Day and Exploited Vulnerabilities Guide is that urgency should be driven by confirmed exploitation, not by severity alone. Where browser-managed secrets or session material may also be exposed, review whether Top 10 Secrets Management Mistakes applies to saved credentials, tokens, or overly persistent access material on affected endpoints.

What to check after you contain it

Once exposure is reduced, look for evidence that the vulnerability may already have been used on systems that were reachable before remediation. In practice, that means reviewing browser, endpoint, EDR, and proxy telemetry for suspicious process launches, unexpected downloads, new persistence, or follow-on activity that would indicate remote code execution was achieved.

Also check whether the vulnerable browser was part of a chain that exposed broader organisational access, because a browser exploit often matters most as the first step in a larger compromise. If the endpoint held cached credentials, saved passwords, tokens, or privileged sessions, the impact can extend well beyond the browser itself.

For a compromise-oriented view of how attackers often turn initial access into broader access, The State of NHI & AI Agent Breach Report 2026 provides useful breach-pattern context around credential theft and lateral movement. The same containment logic also applies when legacy browser exposure coexists with secrets sprawl or reused credentials.

Risk and Threat Considerations

Actively exploited browser vulnerabilities are dangerous because they compress the attacker’s job into a single reachable surface, then hand them a route to code execution on user systems. In a legacy browser scenario, the risk is not only compromise of the browser process, but possible pivot into the endpoint, stored credentials, and adjacent enterprise access.

Failure mechanism: A remote attacker delivers content that triggers the memory corruption condition, gains code execution, and then uses the compromised endpoint to steal data, launch additional payloads, or move into internal systems.

Impact: A successful exploit can lead to endpoint compromise, credential exposure, follow-on malware, and broader intrusion, especially where the browser remains available on systems that still trust it for legacy workflows.

Standards & Framework Alignment

This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.

NIST CSF 2.0, 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 CSF 2.0	ID.RA-01 — Asset Vulnerability Identification	This CVE question requires identifying exposed assets and vulnerable software.
	PR.AA-05 — Identity Management, Authentication, and Access Control	Browser compromise can expose access paths and sessions that rely on user identity.
Recommendation — Identify systems still exposing Internet Explorer and track them as vulnerable assets. Restrict high-risk browser access paths and revoke exposed sessions where compromise is suspected.
NIST SP 800-53 Rev 5	SI-2 — Flaw Remediation	The subject is an actively exploited vulnerability requiring urgent remediation.
	SI-4 — System Monitoring	Post-exploit hunting depends on detecting exploit and follow-on activity.
Recommendation — Remediate the flaw immediately across all in-scope systems and track completion. Monitor endpoints and gateways for signs of exploitation and follow-on payloads.
CIS Controls v8	CIS-7 — Continuous Vulnerability Management	This is a vulnerability prioritisation and remediation problem driven by active exploitation.
Recommendation — Prioritise and remediate the CVE using an exposure-based vulnerability workflow.

Practitioner Guidance

What to prioritise: Identify every asset where the affected browser still exists or can be launched, then treat those systems as a distinct remediation queue rather than folding them into generic patching. Legacy software often survives in exceptions, so inventory quality matters as much as the patch itself.

What to verify: Confirm that remediation actually removes exploitable reachability, not just that a ticket was closed. If the browser is disabled by policy, verify that users cannot re-enable it locally and that fallback paths do not reintroduce the same risk.

Practitioner takeaway: For an actively exploited browser CVE, the decisive question is whether any reachable system still allows the exploit path, because containment, exposure reduction, and post-compromise checking matter more than generic patch urgency alone.