Clickonce - CraftedSignal Threat Feed

New Abuse of ClickOnce Technology for Initial Access and Persistence

hello@craftedsignal.io — Sun, 21 Jun 2026 05:32:16 +0000

Recent observations highlight a novel abuse of Microsoft's ClickOnce technology by threat actors, focusing on its features for initial access, execution, and persistence. This technique, reported by CrowdStrike in June 2026, exploits the inherent trust and minimal user interaction required for ClickOnce application deployment. Attackers leverage this to distribute malicious payloads, bypassing common security mechanisms like email filters that scrutinize .exe files but may overlook .application files. The method allows for the deployment of malware without requiring administrative privileges, broadening the scope of potential victims to standard user accounts. Furthermore, ClickOnce's built-in update mechanism is co-opted to maintain remote access, update C2 infrastructure, or facilitate lateral movement, all while masquerading within legitimate Microsoft processes such as rundll32.exe and dfsvc.exe, significantly enhancing stealth and defense evasion capabilities.

Attack Chain

Initial Access via User Interaction: Threat actors convince targets to click on a malicious link or open an .application file, often via misleading buttons or phishing campaigns, initiating a ClickOnce application deployment.
Deployment of Malicious ClickOnce Application: The user interaction triggers the download and execution of a weaponized ClickOnce application, which contains or ultimately delivers the malicious payload.
Execution within Legitimate Processes: The malicious payload is executed within the context of legitimate Microsoft processes, primarily dfsvc.exe (Deployment Services Client) or rundll32.exe, to evade detection.
Persistence via .appref-ms file: A shortcut file with the .appref-ms extension is dropped in the user's Start Menu directory (%Users%\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\) by the ClickOnce framework, ensuring the malicious application can be re-launched.
Utilizing Built-in Update Mechanism: Once persisted, the attacker can push malicious updates to the application's deployment server. When the user next launches the application via the .appref-ms shortcut, the update mechanism fetches and executes the updated malicious payload without further user prompting.
Remote Access and C2 Maintenance: The updated malicious application can establish persistent remote access, update its command and control (C2) infrastructure, or perform other post-exploitation activities like data exfiltration.
Lateral Movement (Potential): Through the maintained remote access and updated C2, attackers can initiate lateral movement within the compromised network.

Impact

Successful exploitation of ClickOnce technology allows attackers to gain persistent access to targeted systems, bypassing traditional security controls and executing payloads under the guise of legitimate Microsoft processes. This enables capabilities such as remote code execution, data exfiltration, and the establishment of long-term command and control. The lack of administrative privilege requirements means a wider range of user accounts are vulnerable. The ease of payload delivery, coupled with the ability to silently update malware, poses a significant risk for continued compromise and facilitates further malicious activities including ransomware deployment or corporate espionage across targeted organizations in various sectors.

Recommendation

Deploy the Sigma rules in this brief to your SIEM and tune for your environment to detect suspicious ClickOnce activity.
Enable Sysmon process-creation and file-event logging to activate the rules above.
Monitor for process creations where dfsvc.exe is the parent and the child process is not a known, legitimate application.
Educate users on the risks associated with clicking on links or opening .application files from untrusted sources, even if they appear to initiate a software installation.
Implement application whitelisting solutions to prevent the execution of unauthorized ClickOnce applications or executables launched by them.

Threat Actors Abuse Microsoft ClickOnce Update Mechanism for Persistent Malware Delivery

hello@craftedsignal.io — Sun, 21 Jun 2026 05:21:58 +0000

Threat actors are increasingly abusing Microsoft's ClickOnce deployment technology, particularly focusing on its update mechanism, to establish persistent malware presence and evade detection. This technique, highlighted by CrowdStrike in June 2026, leverages the user-friendly installation and built-in updating features of ClickOnce to bypass traditional defenses. Attackers lure users into installing seemingly harmless ClickOnce applications, which drop .appref-ms shortcut files in the Start Menu. Subsequently, the threat actors can push malicious updates to these applications from their controlled deployment servers. This allows for silent malware updates, C2 address changes, and lateral movement capabilities, all while operating within legitimate Microsoft processes like dfsvc.exe and rundll32.exe. This abuse takes advantage of a general lack of awareness around ClickOnce security, providing a stealthy and persistent vector on enterprise endpoints.

Attack Chain

Initial Access via Social Engineering: The attacker convinces a target user, often through phishing emails or malicious websites, to click a link or button that initiates a ClickOnce application download.
Malicious ClickOnce Application Deployment: The user's interaction triggers the download and execution of a malicious .application file, initiating the ClickOnce deployment process.
Execution via Legitimate Processes: The malicious payload executes within legitimate Microsoft process trees, specifically utilizing dfsvc.exe (ClickOnce Deployment Support Service) and rundll32.exe to launch the initial malicious components.
Persistence through .appref-ms File: If the application is configured for offline availability, a shortcut file (.appref-ms) is dropped into the user's Start Menu (%Users\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\).
Malicious Update Delivery: When the user subsequently launches the application via the .appref-ms shortcut, the ClickOnce client checks for updates from the attacker-controlled server.
Silent Payload Update and Re-execution: The attacker pushes a malicious update to the deployment server, which is then downloaded and executed by the dfsvc.exe process without requiring user re-authorization or prompting.
Impact (Remote Access/Lateral Movement): The updated malicious payload can then establish remote access, modify C2 addresses, facilitate lateral movement, or perform other malicious actions on the compromised system.

Impact

The successful exploitation of ClickOnce's update mechanism allows threat actors to maintain persistent access to targeted systems with high stealth. Because the initial application deployment does not require administrative privileges, standard user accounts, which comprise the majority of enterprise endpoints, are vulnerable. Once established, attackers can silently update their malware, enabling them to alter C2 infrastructure, facilitate lateral movement within a network, and exfiltrate sensitive data. This technique bypasses common email gateway protections and traditional file-based scrutiny, leading to extended dwell times and increased potential for significant data breaches or system compromise.

Recommendation

Implement a robust Endpoint Detection and Response (EDR) solution: Deploy EDR capabilities to detect suspicious process creation and network connections from dfsvc.exe and rundll32.exe as detailed in the Sigma rules below.
Deploy the Sigma rules in this brief to your SIEM/EDR: Tune the provided rules to detect dfsvc.exe spawning unusual child processes or making suspicious network connections, and rundll32.exe executing with abnormal parameters.
Monitor process_creation events: Specifically watch for instances where dfsvc.exe or rundll32.exe act as parent processes for scripting interpreters (e.g., powershell.exe, cmd.exe) or other unusual executables.
Monitor network_connection events: Focus on outbound connections initiated by dfsvc.exe to non-standard ports or suspicious external IP addresses/domains.
Educate users on ClickOnce risks: Increase awareness about the nature of .application files and the potential risks of installing software from untrusted sources, even if the installation appears to be legitimate.

Abuse of Microsoft ClickOnce Technology for Malware Deployment

hello@craftedsignal.io — Sat, 20 Jun 2026 15:38:30 +0000

Microsoft's ClickOnce technology, intended to streamline application distribution and updates, is being increasingly abused by threat actors to deploy malicious software. ClickOnce facilitates the deployment of applications with minimal user interaction and often without requiring administrative privileges, making it an ideal vector for malware. This allows adversaries to package and distribute their payloads in a user-friendly format, potentially bypassing traditional security controls. While Part 1 of this research focuses on the internal workings of ClickOnce, it highlights features such as self-contained packaging and self-updating functionality which, if weaponized, could enable persistent and evasive malware campaigns. This abuse poses a significant risk to organizations, as it simplifies the initial access and execution phases for attackers by leveraging a legitimate Microsoft deployment mechanism.

Attack Chain

Threat actor packages a malicious application using Microsoft's ClickOnce publishing tools in Visual Studio.
The actor hosts the generated ClickOnce deployment files (e.g., .application manifest, executable, .deploy files) on a remote web server or network share.
The attacker creates a malicious link, often embedded in a phishing email or hosted on a compromised website, to trigger the download and deployment of the ClickOnce application.
A user clicks the malicious link, which initiates the download of the .application deployment manifest.
The Windows operating system's ClickOnce deployment service (dfsvc.exe) processes the manifest and, if the publisher's signature is not verified, prompts the user for confirmation.
Upon user confirmation, dfsvc.exe downloads and executes the packaged malicious application.
The malicious application runs with the user's privileges, potentially performing actions such as data exfiltration or installing additional malware.
If configured for installation, the malicious ClickOnce application might establish persistence (e.g., via startup entries) and use ClickOnce's self-updating feature for dynamic command and control.

Impact

The abuse of ClickOnce technology allows attackers to easily distribute malware, potentially leading to widespread infections. Because ClickOnce applications often run without requiring administrative privileges, they can bypass security measures that rely on privilege escalation detection. Successful exploitation can result in unauthorized access, data theft, further system compromise, and the deployment of ransomware or other destructive payloads. The self-updating nature of ClickOnce applications means that initially deployed malware can evolve, receive new capabilities, or evade detection over time, making long-term compromise more likely.

Recommendation

Deploy the Sigma rule "Detect ClickOnce Deployment Service Launching Applications" to monitor dfsvc.exe activity for suspicious application launches.
Implement the Sigma rule "Detect Download of Suspicious ClickOnce Deployment Files" to identify .application or .manifest files downloaded from unusual sources.
Use the Sigma rule "Detect ClickOnce Application Execution from Suspicious Paths" to flag executions of ClickOnce apps from temporary or user-controlled directories.
Educate users on the risks associated with installing unsigned or untrusted applications via ClickOnce prompts.
Enable comprehensive process creation logging for dfsvc.exe to capture command-line arguments and parent-child process relationships.

Potential Abuse of Microsoft ClickOnce Technology for Malware Delivery

hello@craftedsignal.io — Fri, 19 Jun 2026 04:55:22 +0000

CrowdStrike has highlighted the potential for abuse of Microsoft's ClickOnce technology, a deployment mechanism designed to simplify application distribution and installation on Windows systems. While ClickOnce offers developers an easy way to package and deliver software, requiring minimal user interaction and no administrative privileges, these very features can be weaponized by threat actors. This initial analysis focuses on the underlying mechanics of ClickOnce deployment, setting the stage for understanding how malicious actors could leverage it to bypass traditional security measures. The user-friendly "click once" installation process means that unsuspecting victims could inadvertently deploy malware, making it a powerful vehicle for initial access and execution. This vulnerability is significant for defenders as it represents a novel or under-documented method for adversaries to achieve their objectives without relying on more commonly detected techniques.

Attack Chain

Preparation: Attacker crafts a malicious application and publishes it using ClickOnce technology, generating a deployment file (e.g., a .application file).
Delivery: The attacker hosts the malicious ClickOnce deployment file on a controlled website or delivers it via a malicious link in a phishing email or message.
User Execution: A victim is lured into clicking the malicious link or opening the deployment file, which triggers its download and initiates the ClickOnce deployment process.
Security Prompt: The operating system displays a security warning or confirmation dialog to the user, particularly if the application publisher's signature is untrusted or unknown.
Deployment Service Invocation: Upon user confirmation, the Windows Deployment Foundation Services (dfsvc.exe) process is invoked to handle the download and installation/execution of the ClickOnce application.
Application Cache Write: The malicious ClickOnce application's files are downloaded and written to the user's ClickOnce application cache, typically located in %LOCALAPPDATA%\Apps\2.0\.
Malware Execution: The malicious ClickOnce application is launched, executing its payload which could include installing additional malware, establishing persistence, or performing data exfiltration.

Impact

If successfully abused, the ClickOnce technology can lead to widespread malware infections, enabling attackers to establish a foothold on victim systems without requiring elevated privileges. Organizations could face data breaches, ransomware attacks, or system compromise as malicious applications bypass conventional security controls. The user-friendly nature of ClickOnce deployment lowers the barrier for successful social engineering, increasing the likelihood of successful attacks across various sectors. While specific victim counts are not available for this abuse method in this part of the research, the potential impact is broad, affecting any Windows environment where users might encounter and execute ClickOnce applications.

Recommendation

Deploy the Sigma rules in this brief to your SIEM and tune for your environment, specifically focusing on process_creation and network_connection logs related to ClickOnce.
Enable comprehensive process_creation logging to capture executions of dfsvc.exe and any processes launched from the ClickOnce application cache (%LOCALAPPDATA%\Apps\2.0\).
Monitor network_connection logs for outbound connections initiated by dfsvc.exe or other ClickOnce-related processes to suspicious or untrusted domains.
Educate users about the risks of executing applications from untrusted sources, even those presented through what appears to be a legitimate Windows installation wizard, as this relates to the Attack Chain step of "Security Prompt".