CVE-2023-24880: Windows 10 1607 SmartScreen Auth Bypass

CVE-2023-24880 Overview

CVE-2023-24880 is a Windows SmartScreen Security Feature Bypass Vulnerability that allows attackers to circumvent the Mark of the Web (MOTW) security mechanism in Windows. This vulnerability enables malicious files downloaded from the internet to bypass SmartScreen warnings and protections, which are designed to alert users about potentially dangerous content. Attackers exploiting this flaw can craft files that appear safe to the operating system, effectively disabling a critical layer of defense against malware distribution.

Critical Impact

This vulnerability is actively exploited in the wild and listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Attackers can deliver malware that completely bypasses Windows SmartScreen protections, allowing malicious payloads to execute without user warnings.

Affected Products

• Microsoft Windows 10 1607, 1809, 20H2, 21H2, 22H2
• Microsoft Windows 11 21H2, 22H2
• Microsoft Windows Server 2016, 2019, 2022

Discovery Timeline

• March 14, 2023 - CVE-2023-24880 published to NVD
• October 27, 2025 - Last updated in NVD database

Technical Details for CVE-2023-24880

Vulnerability Analysis

This security feature bypass vulnerability stems from improper authorization handling (CWE-863) in the Windows SmartScreen component. When files are downloaded from the internet or received via email, Windows normally applies the Mark of the Web (MOTW) attribute, which triggers SmartScreen to display warnings when users attempt to execute these files. The vulnerability allows attackers to craft specially structured files that fail to trigger the MOTW security checks, enabling malicious content to execute silently.

The attack requires local access and user interaction—typically, a victim must be convinced to open a malicious file. However, once executed, the payload runs without the protective warnings that would normally alert users to potential threats. This makes the vulnerability particularly dangerous in phishing campaigns where attackers distribute malware through email attachments or malicious downloads.

Root Cause

The root cause lies in incorrect authorization logic (CWE-863) within Windows SmartScreen's file validation process. The component fails to properly enforce security checks on certain file types or file structures, allowing attackers to create files that are incorrectly classified as safe. This authorization bypass means that the MOTW mechanism, which should mark all internet-downloaded files for additional scrutiny, can be circumvented through specific file crafting techniques.

Attack Vector

This vulnerability requires local access to the target system (AV:L) with user interaction. The typical attack scenario involves:

1. An attacker crafts a malicious file designed to bypass SmartScreen protections
2. The file is delivered to the victim via phishing email, malicious website download, or other social engineering methods
3. The victim downloads and opens the file
4. Due to the MOTW bypass, Windows does not display the expected security warning
5. The malicious payload executes without user awareness of the threat

The vulnerability has been actively exploited in the wild to distribute various malware families, including ransomware. Threat actors leverage this bypass to improve the success rate of their campaigns by eliminating the security friction that would normally warn users.

Detection Methods for CVE-2023-24880

Indicators of Compromise

• Executable files or scripts being executed without Zone.Identifier alternate data streams despite being recently downloaded from external sources
• Unusual file execution patterns from browser download directories or email attachment locations without corresponding SmartScreen events
• Presence of files with malformed or missing MOTW attributes in common download locations

Detection Strategies

• Monitor Windows Event Logs for anomalies in SmartScreen protection events, particularly missing or unexpected application reputation checks
• Deploy endpoint detection rules that identify file executions from internet download zones that lack corresponding SmartScreen verification events
• Implement behavioral analysis to detect post-exploitation activities following execution of files from untrusted sources

Monitoring Recommendations

• Enable enhanced logging for Windows Defender SmartScreen and Application Guard events
• Configure alerts for high-volume file executions from user download directories without MOTW validation
• Utilize SentinelOne Singularity platform to detect behavioral indicators of SmartScreen bypass attempts and subsequent malicious activity

How to Mitigate CVE-2023-24880

Immediate Actions Required

• Apply the Microsoft security update for CVE-2023-24880 immediately on all affected Windows systems
• Prioritize patching internet-facing systems and endpoints that commonly handle downloaded files or email attachments
• Review and enhance email security controls to filter potentially malicious attachments before delivery
• Educate users about the elevated risk of opening unexpected files, even if no warning appears

Patch Information

Microsoft has released security updates to address this vulnerability. Organizations should apply the patches available through the Microsoft Security Update Guide. Given that this vulnerability is listed in the CISA Known Exploited Vulnerabilities Catalog, federal agencies and critical infrastructure organizations are required to remediate within CISA-mandated timelines.

Workarounds

• Implement strict application whitelisting policies using Windows Defender Application Control (WDAC) or AppLocker to prevent unauthorized executables from running
• Configure Group Policy to enhance Mark of the Web enforcement and block execution of files without proper MOTW attributes
• Deploy additional endpoint protection solutions that perform independent file reputation checks beyond SmartScreen
• Restrict execution of scripts and macros from downloaded files through enterprise policy controls

# PowerShell: Verify SmartScreen is enabled via Group Policy
Get-ItemProperty -Path "HKLM:\SOFTWARE\Policies\Microsoft\Windows\System" -Name "EnableSmartScreen" -ErrorAction SilentlyContinue

# Enable SmartScreen enforcement through registry if not managed by Group Policy
Set-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer" -Name "SmartScreenEnabled" -Value "RequireAdmin"