CVE-2024-29988

What it actually does

CVE-2024-29988 is a Windows SmartScreen security feature bypass. A crafted file or shortcut delivered from the internet can avoid the expected SmartScreen warning or reputation prompt, allowing untrusted content to be opened and executed with the privileges of the logged-in user. The vulnerability does not by itself grant remote code execution without user interaction, but it removes a key Windows protection that normally interrupts execution of suspicious downloaded content. In practical attacks, this can enable malware execution, credential theft, payload staging, lateral movement tooling, and broader compromise of confidentiality, integrity, and availability.

Why it matters to the business

Successful exploitation can turn routine phishing or web-download activity into malware execution because users may not see the normal Windows warning that a file is unsafe. This affects widely deployed Windows 10, Windows 11, Windows Server 2019, and Windows Server 2022 systems, creating broad operational exposure across workstations and servers where users can open files or browse the web. The issue is listed in CISA KEV with a remediation due date of 2024-05-21, has active in-the-wild exploitation, and has a high EPSS likelihood, so unpatched systems should be treated as high-priority exposure even though ransomware use is not specifically indicated in the provided data.

How an attack unfolds

An attacker prepares a specially crafted internet-delivered file, shortcut, or container intended to bypass SmartScreen handling. The attacker hosts it on a website, file-sharing service, email attachment, collaboration message, or remote share and persuades a user to open it. On a vulnerable Windows system, the file opens without the SmartScreen prompt or reputation warning that would normally alert or block the user. The opened content then launches attacker-controlled commands or a secondary payload under the user’s privileges. From there, the attacker may download additional malware, establish persistence, steal browser or application credentials, enumerate the environment, or use the initial foothold for further compromise. The provided threat-actor field does not identify a named group, but the vulnerability is confirmed as exploited in the wild.

How to fix it

Apply the Microsoft security updates released in April 2024 or any later cumulative security update for all affected Windows versions, including Windows 10 1809, 21H2, 22H2; Windows 11 23H2; Windows Server 2019; and Windows Server 2022, including 23H2. Because no exact fixed build list was provided, use Microsoft’s official update channels, WSUS, Intune, Configuration Manager, or other patch management tooling to confirm systems have the April 2024 cumulative update or newer. Keep Microsoft Defender Antivirus and SmartScreen enabled and current. As compensating controls, restrict execution of internet-delivered shortcuts and scripts, preserve Mark-of-the-Web metadata, block high-risk attachment types at mail and web gateways, disable or limit outbound SMB/WebDAV where not required, and use attack surface reduction rules or application control to prevent downloaded content from launching scripting engines, command shells, or LOLBins.

How to confirm the fix worked

Confirm that each affected Windows endpoint and server has the April 2024 or later cumulative security update installed. Validate through centralized patch inventory, Microsoft update compliance reporting, vulnerability scanners, or local checks such as installed hotfix/update history and OS build verification against Microsoft release notes. Confirm SmartScreen, Microsoft Defender reputation-based protection, and cloud-delivered protection are enabled. Test security controls with benign internet-downloaded files to verify Mark-of-the-Web is preserved and SmartScreen/Defender telemetry is generated as expected. Run vulnerability scans after patching and ensure no Windows 10, Windows 11, Windows Server 2019, or Windows Server 2022 assets remain flagged as exposed.

Typical attack path

1. Attacker crafts a file or shortcut designed to bypass Windows SmartScreen reputation prompts.
2. Attacker delivers the file through phishing, malicious links, file-sharing platforms, collaboration tools, or compromised websites.
3. User opens the file on an unpatched Windows system.
4. SmartScreen warning or reputation enforcement is bypassed, reducing user-visible friction.
5. The file launches a payload or retrieves additional attacker-controlled content.
6. Payload runs with the privileges of the user who opened the file.
7. Attacker performs follow-on actions such as credential theft, persistence, discovery, command-and-control, or lateral movement.

How to detect it

Investigate whether exploitation already occurred by correlating user file-open events with suspicious process creation, network connections, and malware detections. Review EDR telemetry, Windows Security logs with process creation enabled, Sysmon events, Microsoft Defender for Endpoint alerts, SmartScreen and Defender operational logs, email gateway logs, web proxy logs, DNS logs, and file-system telemetry. Focus on activity after delivery of internet-downloaded files, especially shortcut or archive content that caused explorer.exe, a browser, or an archive utility to spawn command shells, script interpreters, mshta, rundll32, regsvr32, curl, certutil, bitsadmin, or PowerShell. Look for files lacking expected Mark-of-the-Web metadata when downloaded from external sources, unusual Zone.Identifier alternate data stream patterns, and outbound connections to newly registered, low-reputation, or file-hosting domains immediately after the file was opened. Because this vulnerability is a bypass rather than a malware family, there is no single universal IOC; detection should emphasize execution chains and artifacts showing internet-sourced content led directly to payload execution.

• [InternetShortcut]
• URL=file://
• URL=\\
• Zone.Identifier
• [ZoneTransfer]
• ZoneId=3
• explorer.exe
• powershell.exe
• cmd.exe
• wscript.exe
• cscript.exe
• mshta.exe
• rundll32.exe
• regsvr32.exe
• certutil.exe
• bitsadmin.exe
• curl.exe
• Microsoft-Windows-Sysmon/Operational Event ID 1
• Microsoft-Windows-Sysmon/Operational Event ID 3
• Microsoft-Windows-Sysmon/Operational Event ID 11
• Microsoft-Windows-Sysmon/Operational Event ID 15
• Windows Security Event ID 4688

What your security team should do

• Immediately identify all affected Windows 10, Windows 11, Windows Server 2019, and Windows Server 2022 systems that have not received the April 2024 or later cumulative update.
• Prioritize remediation for internet-facing systems, user workstations, administrator workstations, jump hosts, and systems used for email, browsing, or file handling.
• Meet or exceed the CISA KEV remediation urgency; the listed due date was 2024-05-21 and the vulnerability is actively exploited in the wild.
• Hunt for suspicious execution chains where explorer.exe or a browser opens downloaded shortcut, script, archive, or document content that spawns cmd.exe, powershell.exe, wscript.exe, cscript.exe, mshta.exe, rundll32.exe, regsvr32.exe, or other living-off-the-land binaries.
• Review email, web proxy, EDR, and file telemetry for suspicious internet-delivered shortcut files or archives opened by users shortly before malware detections or outbound command-and-control traffic.
• Enforce SmartScreen, Defender cloud protection, attack surface reduction rules, and application control policies for high-risk file types.
• Restrict or monitor outbound SMB and WebDAV access to untrusted destinations, especially following user interaction with downloaded files.
• Educate helpdesk and incident response teams that absence of a SmartScreen warning does not prove downloaded content was safe on unpatched systems.