CVE-2023-24880: Critical Windows SmartScreen Security Bypass Advisory and Analysis
Microsoft Windows SmartScreen contains a security feature bypass vulnerability that could allow an attacker to evade Mark of the Web (MOTW) defenses via a specially crafted malicious file.
FREQUENTLY ASKED
What is CVE-2023-24880 and why does it matter?
CVE-2023-24880 is a security feature bypass vulnerability in Microsoft Windows SmartScreen. It matters because it allows attackers to evade the Mark of the Web (MOTW) defenses. This vulnerability is actively exploited in the wild and has been linked to ransomware campaigns, making it a significant risk to organizational integrity despite its Medium CVSS score.
Which versions of Windows are affected by CVE-2023-24880?
The vulnerability affects multiple versions of the Windows operating system, including Windows 10 versions 10.0.17763.0, 10.0.19043.0, 10.0.19045.0, 10.0.14393.0, as well as Windows 11 version 10.0.22621.0 and Windows Server version 10.0.20348.0. All users running these base builds should verify their specific patch levels against the March 2023 updates.
Has a patch been released for CVE-2023-24880?
Yes, Microsoft released an official patch for CVE-2023-24880 on March 14, 2023. The fix is included in the cumulative security updates for that month. Administrators can access the update guide via the Microsoft Security Response Center (MSRC) to download the necessary security packages for their specific environment.
What is the remediation deadline and what does it mean for compliance?
The remediation deadline for CVE-2023-24880 is April 4, 2023. For federal agencies and organizations following CISA's Known Exploited Vulnerabilities (KEV) catalog mandates, this date is a strict deadline for applying patches. Failure to meet this deadline results in non-compliance with BOD 22-01 and leaves systems exposed to active exploitation.
How can I check if my Windows deployment is affected?
To check if an instance is affected, administrators should verify the current build number and update history of their Windows systems. If the system has not applied the March 2023 cumulative updates (or later), it remains vulnerable. Automated vulnerability scanners and Microsoft Endpoint Manager can also be used to identify systems missing the patch for CVE-2023-24880.
CVE-2023-24880 represents a significant security feature bypass in Microsoft Windows SmartScreen (CWE-863). With a CVSS score of 4.4 (Medium), the vulnerability's impact is amplified by its active exploitation in the wild, particularly within ransomware delivery chains. Organizations must prioritize the remediation deadline of April 4, 2023, to mitigate the risk of targeted attacks that utilize specially crafted files to circumvent the Windows Mark of the Web (MOTW) security mechanism.
Vulnerability Profile
Field
Value
CVE ID
CVE-2023-24880
Affected Product & Versions
Windows 10 (17763.0, 19043.0, 19045.0, 14393.0), Windows 11 (22621.0), Windows Server (20348.0)
Technical Deep Dive: Understanding CWE-863 and the MOTW Bypass
At the core of CVE-2023-24880 is CWE-863: Incorrect Authorization, specifically applied to how Windows SmartScreen handles the "Mark of the Web" (MOTW). MOTW is a security feature that tags files downloaded from the internet (the "Untrusted Zone") with an NTFS Alternative Data Stream (ADS) named Zone.Identifier. When a user attempts to execute a file with this tag, Windows triggers SmartScreen to scan the file and display a warning if the file is unsigned or known to be malicious.
The Attack Mechanism
In this specific vulnerability, attackers use a specially crafted file—often a malformed Authenticode signature—to trick the system's authorization logic. By exploiting how Windows parses file signatures during the MOTW check, the attacker ensures that the operating system fails to correctly identify the file as needing a SmartScreen prompt. This is a "logic failure" rather than a memory corruption issue.
Think of MOTW as a security checkpoint at an airport. Normally, everyone coming from an international flight (the internet) must go through a scan. CVE-2023-24880 is akin to a traveler showing a specifically "glitched" passport that causes the security gate to simply remain open without triggering the scanner. Because the gate doesn't close, the security personnel (SmartScreen) never get the chance to intervene.
Surface and Blast Radius
The attack surface is local, meaning the victim must download and interact with a malicious file. However, because the attack complexity is low and no special privileges are required, it is highly effective in phishing campaigns. The blast radius involves the initial execution of arbitrary code, which is the primary gateway for ransomware deployment. The EPSS score of 0.73308 (placing it in the 98.8th percentile of all vulnerabilities) highlights that this is not a theoretical risk but a weaponized tool used by threat actors.
Who Is Affected: Impacted Windows Versions and Compliance
This vulnerability impacts a wide range of Windows ecosystems. Notable affected versions include:
Windows 10: Specifically builds 10.0.17763.0, 10.0.19043.0, 10.0.19045.0, and 10.0.14393.0.
Windows 11: Build 10.0.22621.0.
Windows Server: Build 10.0.20348.0.
Compliance Mandate (CISA BOD 22-01)
Because CVE-2023-24880 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, it carries a mandatory remediation deadline for US Federal Executive Branch agencies under Binding Operational Directive (BOD) 22-01. The deadline is April 4, 2023. Private sector organizations are strongly encouraged to align with this timeline, as the vulnerability is a known component of active ransomware operations.
Official Remediation Steps
To secure your systems against CVE-2023-24880, follow these remediation steps:
Identify Vulnerable Assets: Use Microsoft Endpoint Configuration Manager, WSUS, or a third-party vulnerability management tool to identify Windows 10, 11, and Server instances missing the March 2023 updates.
Apply Cumulative Updates: Ensure that the March 14, 2023 (or newer) cumulative update is installed. These updates contain the logic fixes required to correctly parse file signatures and enforce SmartScreen MOTW checks.
Verify Patch Status: After installation and a system restart, verify that the OS build number matches the patched version specified in the Microsoft documentation.
Monitor for MOTW Bypass Attempts: Utilize Endpoint Detection and Response (EDR) tools to monitor for unusual file execution patterns that bypass traditional SmartScreen warnings.
Security Best Practices for Windows Environments
Addressing CWE-863 and similar bypasses requires a defense-in-depth strategy beyond simple patching:
Enforce Application Control: Use AppLocker or Windows Defender Application Control (WDAC) to restrict the execution of unsigned binaries, regardless of whether they trigger a SmartScreen prompt.
Implement Cloud-Delivered Protection: Ensure Windows Defender Cloud-Delivered Protection is enabled. This provides real-time analysis of files that may attempt to circumvent local logic checks.
Disable Unnecessary File Types: Use Group Policy Objects (GPO) to prevent the execution of risky file types (like .iso, .vhd, .js, or .vbs) directly from the internet or temporary folders.
User Awareness Training: Train users to be suspicious of any downloaded file that asks them to perform unusual actions, such as extracting a file from a password-protected ZIP, which is a common tactic to bypass scanners.
Enhance Email Filtering: Utilize advanced email security gateways to strip suspicious attachments before they reach the user's inbox, reducing the likelihood of a user interacting with a crafted file.
Audit Zone Identifier Application: Regularly audit system logs to ensure that MOTW identifiers are being correctly applied to downloaded files, and investigate any anomalies where downloads appear without a Zone.Identifier stream.