How do you patch or mitigate CVE-2015-0071 (Microsoft Internet Explorer ASLR Bypass)?

CISA’s required action for CVE-2015-0071 is to apply updates per vendor instructions. In practice, find every instance of Microsoft Internet Explorer in your estate, apply the vendor security update or documented mitigation, and if no fix can be applied, remove internet exposure or take the product out of service. After patching, review logs for signs of earlier exploitation, because attackers used this flaw in the wild.

What changes when you have to patch an exploited browser ASLR bypass?

CVE-2015-0071 is not a “tune the browser settings” issue. The practical change is that you need to treat Internet Explorer as an exposed exploit path, verify where it still exists, and remove or contain it quickly if you cannot remediate immediately. Because this was used in the wild, the response has to combine patching with exposure reduction and compromise review.

For patch execution, the starting point is asset discovery and update validation: confirm which endpoints still have Microsoft Internet Explorer installed or enabled, then apply the vendor security update exactly as directed by Microsoft and CISA. If the environment cannot take the update right away, the fallback is to reduce exposure by disabling access to the product, restricting internet use, or removing it from service until the fix can be applied.

That response pattern is the same discipline recommended in Vulnerability Management Guide: know your exposure, prioritize confirmed exploitation, and verify the remediation actually landed rather than assuming a package rollout solved the problem.

For browser-specific hardening and containment, the relevant lesson is that legacy browser surface area should be treated as a managed risk, not a convenience feature. NHIMG’s Enterprise Browser and Browser Security Guide is useful here because browser policy, isolation, and managed controls are often the difference between a temporary mitigation and a recurring exposure.

How do you confirm exposure and limit blast radius before and after the fix?

Confirm exposure by checking more than installed software lists. You want to know whether Internet Explorer can still launch, whether it is reachable by users or automation, and whether any business process still depends on it. If the browser is present only for compatibility but not needed for ordinary work, that is often the fastest candidate for removal, disablement, or isolation.

When the patch cannot be applied immediately, limit blast radius by shrinking the paths through which the vulnerable browser can be reached. That can mean blocking external web access from affected systems, confining use to a tightly controlled segment, or taking the application stack that depends on it out of service until the update is deployed. The core decision is simple: if you cannot close the flaw, you must close the exposure.

Use authoritative vulnerability records to confirm the remediation target and track the issue state. The CISA Known Exploited Vulnerabilities Catalog is the right place to verify that the item is being treated as actively exploited, while the CVE Program provides the canonical vulnerability identifier and record structure.

The operational point is that mitigation should be specific to the actual deployment model. A workstation browser, a locked-down kiosk, and an application compatibility host do not deserve the same control choice if business continuity is at stake.

What should you check for after patching or mitigation?

After remediation, review logs for signs that the flaw was already used. Because the issue was exploited in the wild, post-fix review should not be limited to “did the update install successfully?” You are looking for suspicious browser activity, unexpected child processes, unusual outbound connections, and any change around the time the vulnerable browser was exposed.

If you find indicators of earlier compromise, escalate beyond patching. That can require broader host investigation, credential review, and containment of adjacent systems if the browser was one step in a larger intrusion chain. Even when no evidence of abuse is found, keep the record of what was patched, when it was verified, and which systems were excluded or retired so the same exposure does not silently return later.

Attack-path thinking is valuable here, and MITRE ATT&CK Enterprise Matrix helps teams map browser exploitation, execution, and follow-on activity into a detection workflow rather than treating the CVE as a one-off patch ticket.

For prioritization, FIRST EPSS is a useful complement when you are deciding how aggressively to schedule verification and hunting across a large fleet, especially when multiple exploitable issues compete for the same maintenance window.

Risk and Threat Considerations

The main risk is not the browser itself, but the combination of a widely deployed client, an in-the-wild exploitation history, and the possibility that remediation is delayed on business-critical endpoints. A bypass of address space protection can make exploit chains more reliable, which increases the value of the issue to attackers looking for initial access or follow-on compromise.

Failure mechanism: If the vulnerable browser remains installed and reachable, an attacker can use the bypass as part of an exploitation chain that weakens exploit resistance and improves the chance of successful code execution or intrusion.

Impact: Successful abuse can lead to browser compromise, user-session abuse, endpoint foothold, and a wider incident if the browser is allowed to reach sensitive internal or internet-facing resources.

Standards & Framework Alignment

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

CIS Controls v8 and NIST SP 800-53 Rev 5 set the governance and control requirements practitioners need to meet.

Framework	Control / Reference	Relevance
CIS Controls v8	CIS-7 — Continuous Vulnerability Management	The subject is active vulnerability remediation and verification.
	CIS-18 — Penetration Testing	Post-exploitation review and validation benefit from adversary-path checking.
Recommendation — Prioritise, patch, and verify exposed Internet Explorer instances quickly. Use validation and testing to confirm the bypass is no longer exploitable.
NIST SP 800-53 Rev 5	RA-5 — Vulnerability Monitoring and Scanning	The answer depends on finding affected hosts and tracking remediation status.
	SI-2 — Flaw Remediation	The core action is applying vendor updates or documented mitigations.
	AU-6 — Audit Record Review, Analysis, and Reporting	The question explicitly asks to review logs after patching for earlier exploitation.
Recommendation — Scan for Internet Explorer exposure and track remediation to closure. Apply the vendor fix or approved mitigation and verify deployment. Review audit data for signs of exploitation before and after remediation.

Practitioner Guidance

What to prioritise: Patch Internet Explorer wherever it still exists, but treat systems that cannot be updated as a containment problem, not a delay problem. If the browser is needed only for legacy compatibility, isolate it and reduce internet reach immediately.

What to verify: Confirm the vendor update or documented mitigation actually changed the affected estate, then validate that the vulnerable browser is no longer usable for ordinary browsing on those systems. Verification matters as much as installation because rollback, alternative launch paths, and unmanaged hosts are common failure points.

Practitioner takeaway: For an exploited browser CVE, the real control is not “patch later”, it is “patch fast, contain anything that cannot be patched, and look for evidence the weakness was already used.”