CVE-2023-24880: Microsoft Windows SmartScreen Security Feature Bypass Vulnerability

CVE-2023-24880 is a security feature bypass in Microsoft Windows SmartScreen. It can let an attacker evade Mark of the Web (MOTW) protections by delivering a specially crafted malicious file. Because MOTW is a common Windows defense that flags files from untrusted sources and triggers extra scrutiny or blocking, a bypass of this kind matters for endpoint security. CISA notes known ransomware use of this vulnerability, so organizations should treat it as a priority for Windows fleets.

Public detail is limited to the class of issue and the high-level impact described by CISA. Exact affected builds, exploit mechanics, and scoring must be confirmed against the Microsoft vendor advisory.

How it works

The underlying weakness is CWE-863 (Incorrect Authorization). In this case, SmartScreen fails to correctly enforce authorization checks tied to Mark of the Web. MOTW is an alternate data stream Windows applies to files downloaded from the internet or other untrusted origins; SmartScreen and related components use it to decide whether to warn the user, block execution, or apply additional policy.

An attacker abuses the flaw by crafting a malicious file that causes SmartScreen to skip or mis-handle the MOTW evaluation. The result is that a file which should have been treated as untrusted may run with fewer warnings or restrictions. No further exploit specifics are provided in the available facts; defenders should assume a specially crafted file is the delivery vehicle and should not invent payload details. Confirm the precise conditions and any prerequisites in the vendor advisory.

Am I affected? How to find it in your systems

The vulnerability affects Microsoft Windows systems that use SmartScreen. SmartScreen is present on modern Windows client and server editions that handle user-downloaded content, email attachments, or files from removable or network sources. Inventory every Windows endpoint and server that processes untrusted files.

• Use asset management, configuration management databases, or endpoint management tools (for example, Microsoft Endpoint Manager / Intune, SCCM/MECM, or equivalent) to list Windows versions and patch levels.
• Check whether SmartScreen is enabled via Group Policy, MDM, or local security settings; the feature is commonly on by default for consumer and enterprise images, but custom hardening may alter it.
• Confirm the exact list of affected Windows builds and any required updates only against the Microsoft advisory for CVE-2023-24880; do not rely on third-party version lists.
• For signs of exploitation, review endpoint detection and response (EDR) telemetry for unusual file execution from internet or email sources that lack expected MOTW tags, SmartScreen warnings that were suppressed, or ransomware-related process trees. Windows Event Logs related to SmartScreen, AppLocker/WDAC, and Defender can provide supporting context, but specific event IDs or signatures are not detailed in the facts and must be validated against vendor and CISA guidance.

How to remediate

Patch first. Apply the Microsoft updates for CVE-2023-24880 exactly as directed in the vendor advisory. CISA’s required action is to apply updates per vendor instructions; treat that as the primary remediation step.

• Deploy the security update through your normal Windows Update, WSUS, or enterprise patch pipeline as soon as testing allows.
• After patching, verify SmartScreen and MOTW behavior on representative systems (for example, by downloading a known-safe test file from the internet and confirming the expected zone identifier and SmartScreen response).
• As hardening for this class of issue, keep SmartScreen enabled, enforce MOTW-aware policies (including those that block or sandbox unmarked or internet-origin files), and maintain current Microsoft Defender or equivalent antivirus signatures. Restrict execution of content from untrusted locations via application control (WDAC/AppLocker) where feasible.

If you can't patch immediately

Until the vendor update can be applied, reduce exposure with compensating controls that limit the usefulness of a MOTW bypass.

• Segment high-risk endpoints and restrict outbound and lateral network access so that successful file execution has limited reach.
• Use virtual patching or web/email gateway rules that strip or quarantine suspicious attachments and archives before they reach the endpoint; focus on file types commonly used for initial access.
• Where policy allows, temporarily tighten SmartScreen and MOTW-related Group Policy or MDM settings to the most restrictive supported mode, and disable unnecessary download or auto-execute features.
• Increase monitoring: alert on execution of files lacking MOTW when they originate from email or browser paths, and watch for ransomware indicators (mass file encryption, shadow copy deletion, unusual process trees). Ensure EDR and logging cover these signals.
• Limit user privileges so that even a bypassed MOTW check cannot easily elevate or persist.

These measures lower risk but do not replace the vendor patch. Schedule the update as soon as operational constraints allow.

If your data may have been exposed

Actively exploited vulnerabilities, including those with known ransomware use, frequently lead to breaches. If you suspect this CVE was used against your environment, follow your incident response plan: isolate affected hosts, preserve forensic evidence, and assess for ransomware or data theft. Independently, you can run a free exposure scan of your email address against known breach data to check whether credentials or personal information associated with your accounts have already appeared in public dumps.