ClickOnce

Executive Summary

ClickOnce (T1127.002) is a MITRE ATT&CK technique associated with Stealth, Execution. Adversaries may use ClickOnce applications (.appref-ms and .application files) to proxy execution of code through a trusted Windows utility.(Citation: Burke/CISA ClickOnce BlackHat) ClickOnce is a deployment that enables a user to create self-updating Windows-based .NET applications (i.e, .XBAP, .EXE, or .DLL) that install and run from a file share or web page with minimal user interaction.

Why Attackers Use It

Attackers use ClickOnce because it provides a reliable way to advance their objective within the Stealth, Execution tactic, often with a favorable balance of impact versus detectability on Windows environments. Defenders should assess this behavior in the context of the affected platform and adjacent activity rather than treating it as a standalone indicator.

MITRE Description

Adversaries may use ClickOnce applications (.appref-ms and .application files) to proxy execution of code through a trusted Windows utility.(Citation: Burke/CISA ClickOnce BlackHat) ClickOnce is a deployment that enables a user to create self-updating Windows-based .NET applications (i.e, .XBAP, .EXE, or .DLL) that install and run from a file share or web page with minimal user interaction. The application launches as a child process of DFSVC.EXE, which is responsible for installing, launching, and updating the application.(Citation: SpectorOps Medium ClickOnce)

Because ClickOnce applications receive only limited permissions, they do not require administrative permissions to install.(Citation: Microsoft Learn ClickOnce) As such, adversaries may abuse ClickOnce to proxy execution of malicious code without needing to escalate privileges.

ClickOnce may be abused in a number of ways. For example, an adversary may rely on User Execution. When a user visits a malicious website, the .NET malware is disguised as legitimate software and a ClickOnce popup is displayed for installation.(Citation: NetSPI ClickOnce)

Adversaries may also abuse ClickOnce to execute malware via a Rundll32 script using the command rundll32.exe dfshim.dll,ShOpenVerbApplication1.(Citation: LOLBAS /Dfsvc.exe)

Additionally, an adversary can move the ClickOnce application file to a remote user’s startup folder for continued malicious code deployment (i.e., Registry Run Keys / Startup Folder).(Citation: Burke/CISA ClickOnce BlackHat)(Citation: Burke/CISA ClickOnce Paper)

Attack Flow

1. Attacker gains the prerequisite access or context described below.
2. Attacker executes ClickOnce to achieve its tactical objective (Stealth, Execution).
3. Resulting access/data/effect is leveraged to advance the broader attack chain (see Related Techniques).

Prerequisites

• Platform(s): Windows
• ATT&CK does not define one universal permission requirement for this technique. Establish the required access from the observed implementation and affected platform.

Common Tools

• Tool attribution is implementation-specific. Use ATT&CK procedure examples and local telemetry to identify the binaries, services, scripts, accounts, or cloud resources involved.

Commands

No universal command represents ClickOnce. Capture the exact command line, arguments, parent process, account, host, and execution time from the investigated environment; do not operationalize unverified examples.

Network Traffic

• Network observability is implementation-dependent. Review DNS, proxy, firewall, flow, authentication, and packet telemetry around the activity window, then correlate remote endpoints and protocol behavior with host evidence.

Windows Events

Sysmon Events

Detection Opportunities

No MITRE detection guidance published for this technique.

Relevant ATT&CK Data Sources: N/A

Sigma Rules

A universal Sigma rule would create unreliable results because this technique has no single guaranteed observable. Build detection logic from a documented behavior and supported data source, scope it to the affected platform, and validate it against benign administrative activity before deployment.

Splunk Queries

Start with the data sources named in the detection section. Scope searches by asset, identity, and time window; correlate the primary behavior with preceding access and subsequent actions. A portable query is intentionally not provided where the technique lacks a universal schema or observable.

Investigation Workflow

1. Confirm that the observed behavior is consistent with ClickOnce and rule out expected administrative or application activity.
2. Establish the first-seen time, initiating identity, source system, target system, and affected resources.
3. Collect relevant host, identity, network, cloud, and application telemetry for the surrounding time window.
4. Correlate parent and child activity, remote connections, file or configuration changes, and related ATT&CK techniques.
5. Determine scope by searching for the same observable across peer assets and identities.
6. Preserve volatile evidence and record confidence, assumptions, and telemetry gaps before containment.

Containment

1. Isolate affected host(s)/account(s) identified during investigation.
2. Revoke or rotate any credentials/tokens potentially exposed.
3. Apply the mitigations listed below where not already enforced.
4. Validate no related techniques (see Related Techniques) were chained against the same asset.

Mitigation

• M1042 -- Disable or Remove Feature or Program: Disable or remove unnecessary and potentially vulnerable software, features, or services to reduce the attack surface and prevent abuse by adversaries.
• M1021 -- Restrict Web-Based Content: Restricting web-based content involves enforcing policies and technologies that limit access to potentially malicious websites, unsafe downloads, and unauthorized browser behaviors.
• M1045 -- Code Signing: Code Signing is a security process that ensures the authenticity and integrity of software by digitally signing executables, scripts, and other code artifacts.

Related Techniques

• T1127