How do you patch or mitigate CVE-2018-0824 (Microsoft COM for Windows Deserialization of Untrusted Data)?

CISA’s required action for CVE-2018-0824 is to apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable. In practice, find every instance of Microsoft Windows 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 it means to patch CVE-2018-0824 safely

This CVE is best handled as an exploited Windows deserialization issue, not just a routine patch ticket. The practical objective is to remove exposure on every affected Windows instance, apply Microsoft’s vendor update or mitigation, and verify that the affected systems are no longer reachable in ways that would let an attacker trigger the flaw again.

Because deserialization bugs often support code execution or privilege abuse through crafted input, remediation is only complete when you confirm the vulnerable component is updated and the relevant service path is no longer externally exposed. Insecure Deserialisation Guide is useful background on why untrusted data handling must be treated as an attack surface, not a coding detail.

How to confirm exposure and decide whether mitigation is enough

Start by inventorying Windows systems that use the vulnerable COM path and checking whether the vendor fix is installed. For this class of issue, version guessing is weaker than direct validation, so confirm the exact build state from your management tooling, patch inventory, or host-based compliance checks. If the vendor mitigation is documented but the patch cannot be applied immediately, treat that system as an exception with compensating controls.

If you can confirm the vulnerable software is present and the patch is available, patching is the preferred path. If the patch cannot be deployed, your fallback is to reduce the reachable attack surface as aggressively as possible, especially for any system that is internet-facing or reachable from untrusted networks. CISA Known Exploited Vulnerabilities Catalog is the authoritative place to verify the KEV status and the required remediation posture for this CVE.

When a host cannot be fixed quickly, the important decision is whether the business can tolerate keeping it online under restricted exposure. If the answer is no, discontinuing use is safer than leaving a known exploited deserialization path exposed while waiting for a maintenance window.

What to check after patching or containment

After remediation, review the systems that were exposed before the fix, because in-the-wild exploitation changes the question from “is it patched?” to “was it already used?”. Focus on authentication logs, process creation, unusual child processes, unexpected service behavior, and any signs that the vulnerable component was invoked with attacker-controlled input.

Post-patch review should also include the broader environment around the affected Windows systems. If the flaw was reachable from a service account, remote management path, or application integration, verify whether any credentials, sessions, or persisted access could have been abused during the exposure window. Zero-Day and Exploited Vulnerabilities Guide is a useful companion for the post-remediation step of hunting for evidence of exploitation and closing the remediation loop.

Risk and Threat Considerations

Deserialization flaws are attractive because they can turn trusted application behavior into an execution path for attacker-controlled data. When the vulnerable Windows component is reachable over the network or by a local service with broad privileges, the exposure can extend beyond the original application boundary and into system-level compromise.

Failure mechanism: Crafted input is accepted as if it were trusted serialized data, allowing the attacker to drive unintended object creation or execution logic before defensive checks can intervene.

Impact: The practical consequences are remote code execution, lateral movement, or follow-on compromise of adjacent services, especially if the vulnerable host has long-lived trust relationships or administrative reach.

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	PR.AA-05 — Least Privilege	Windows exposure and containment depend on restricting reachable attack paths and trust relationships.
	DE.CM-01 — Networks and network services are monitored to detect potential cybersecurity events	Post-patch hunting requires monitoring for exploitation and suspicious service activity.
Recommendation — Restrict exposed services and remote access to the smallest necessary set. Monitor network and service activity for exploitation indicators after remediation.
NIST SP 800-53 Rev 5	SI-2 — Flaw Remediation	This CVE requires applying the vendor fix or mitigation to remove the known flaw.
	AU-6 — Audit Record Review, Analysis, and Reporting	Reviewing logs after exploitation is necessary to detect prior compromise.
Recommendation — Apply the vendor patch or approved mitigation without delay. Review audit and system logs for signs of pre-remediation exploitation.
CIS Controls v8	CIS-7 — Continuous Vulnerability Management	The issue is a KEV-listed vulnerability that should be prioritized in vuln management.
	CIS-8 — Audit Log Management	Post-fix investigation depends on available logs and retained evidence.
Recommendation — Prioritize, patch, and verify KEV-listed vulnerabilities first. Preserve and review logs to support compromise assessment.

Practitioner Guidance

What to prioritise: Patch every reachable Windows instance first, then move to containment for anything you cannot patch immediately. Internet-facing hosts, remotely accessible administrative systems, and systems with high-trust service relationships deserve the fastest handling because they create the shortest attack path.

What to verify: Confirm that the mitigation actually removes the reachable exploit path, not just that a change request was closed. If you only reduced exposure, verify the service is no longer externally reachable, the vulnerable function is not callable from untrusted networks, and compensating controls are documented.

Practitioner takeaway: For an exploited Windows deserialization CVE, patching is necessary but not sufficient, because the real security question is whether the system was already reachable and whether it left behind signs of compromise.