CVE-2024-21351: Windows 10 1507 Auth Bypass Vulnerability

CVE-2024-21351 Overview

CVE-2024-21351 is a security feature bypass vulnerability affecting Windows SmartScreen, a built-in security mechanism designed to protect users from malicious applications and websites. This vulnerability allows attackers to bypass SmartScreen's protective warnings, enabling malicious files to execute without the typical security prompts that would alert users to potential threats.

Critical Impact

This vulnerability is actively exploited in the wild and has been added to CISA's Known Exploited Vulnerabilities (KEV) catalog. Attackers can leverage this flaw to deliver malware while bypassing Windows SmartScreen protections, significantly increasing the likelihood of successful compromise.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1809, 21H2, 22H2)
• Microsoft Windows 11 (versions 21H2, 22H2, 23H2)
• Microsoft Windows Server 2016, 2019, 2022, and 2022 23H2

Discovery Timeline

• February 13, 2024 - CVE-2024-21351 published to NVD
• October 28, 2025 - Last updated in NVD database

Technical Details for CVE-2024-21351

Vulnerability Analysis

This vulnerability resides in Windows SmartScreen, a security feature that analyzes downloaded files and applications to determine if they pose a threat. When files are downloaded from the internet, Windows applies a Mark of the Web (MotW) identifier, which triggers SmartScreen to display warning dialogs before execution.

CVE-2024-21351 enables attackers to craft malicious files that evade SmartScreen's protective mechanisms. When successfully exploited, files can execute without displaying the expected security warnings, allowing malware to run with the user's current privileges. The vulnerability requires user interaction—typically convincing a victim to open a specially crafted file—but the absence of SmartScreen warnings significantly lowers user suspicion and increases exploitation success rates.

The vulnerability is classified under CWE-94 (Improper Control of Generation of Code / Code Injection), indicating that the flaw involves improper handling of code or data that allows for injection of malicious content.

Root Cause

The root cause of CVE-2024-21351 lies in improper validation within the SmartScreen feature. The vulnerability allows specially crafted files to bypass the normal inspection process that would typically result in security prompts. This bypass circumvents one of Windows' primary defensive layers against internet-sourced threats, leaving users vulnerable to social engineering attacks that deliver malicious payloads.

Attack Vector

Exploitation of this vulnerability follows a network-based attack vector requiring user interaction. A typical attack scenario involves:

1. An attacker crafts a malicious file designed to bypass SmartScreen protections
2. The file is delivered to victims via email attachments, malicious websites, or compromised download links
3. When the victim opens or executes the file, SmartScreen fails to display the expected warning
4. The malicious payload executes with the victim's privileges, potentially leading to code execution, data theft, or further system compromise

The attack requires no special privileges from the attacker and can be launched remotely over a network connection. The absence of SmartScreen warnings makes it significantly easier for attackers to trick users into executing malicious content.

Detection Methods for CVE-2024-21351

Indicators of Compromise

• Files with missing or manipulated Zone.Identifier alternate data streams that should contain MotW information
• Execution of downloaded executables without corresponding SmartScreen event logs
• Suspicious file downloads from untrusted sources followed by immediate execution
• Anomalous process creation events from files that bypassed SmartScreen verification

Detection Strategies

• Monitor Windows Security event logs for anomalies in SmartScreen events (Event IDs related to SmartScreen decisions)
• Implement endpoint detection rules to identify executables lacking proper MotW attributes
• Deploy behavioral analysis to detect post-exploitation activities following SmartScreen bypass
• Use threat intelligence feeds to identify known malicious file hashes associated with this exploitation technique

Monitoring Recommendations

• Enable and centralize Windows Defender SmartScreen telemetry for analysis
• Configure alerts for high-risk file executions from internet-sourced locations
• Implement user and entity behavior analytics (UEBA) to detect unusual download-to-execution patterns
• Regularly audit endpoint logs for signs of SmartScreen bypass attempts

How to Mitigate CVE-2024-21351

Immediate Actions Required

• Apply Microsoft's security updates released in the February 2024 Patch Tuesday immediately
• Enable Windows Defender Application Control (WDAC) to provide additional execution controls
• Educate users about the risks of opening files from untrusted sources, even if no warning appears
• Review and restrict administrative privileges to limit the impact of potential compromises

Patch Information

Microsoft addressed this vulnerability in the February 2024 security updates. Organizations should apply the relevant patches for their Windows versions immediately, given the active exploitation status. Detailed patch information is available in the Microsoft Security Advisory for CVE-2024-21351. CISA has added this vulnerability to their Known Exploited Vulnerabilities Catalog, requiring federal agencies to remediate by specified deadlines.

Workarounds

• Implement application whitelisting solutions to prevent execution of unauthorized applications
• Configure Group Policy to block execution of files from internet-sourced locations when possible
• Deploy email gateway filtering to block potentially malicious file attachments
• Use network segmentation to limit lateral movement if initial compromise occurs

# Enable Windows Defender SmartScreen via Group Policy
# Path: Computer Configuration > Administrative Templates > Windows Components > Windows Defender SmartScreen
# Set "Configure Windows Defender SmartScreen" to Enabled
# Set action to "Warn and prevent bypass"

# PowerShell command to verify SmartScreen status
Get-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer" -Name SmartScreenEnabled