Suspicious File Download via Headless Browser

Since at least 2025, the DUCKTAIL threat actor has been observed utilizing a deceptive technique involving headless Chromium-based browsers like Microsoft Edge, Google Chrome, Brave, Opera, and Vivaldi. This method automates the download of content from suspicious internet sources using direct URLs or known file-sharing platforms. By launching browsers in --headless mode and employing the --dump-dom argument, DUCKTAIL aims to covertly retrieve additional tools, malware, or sensitive data onto compromised systems without visual user interaction. This tactic enables attackers to maintain a low profile while escalating their control or exfiltrating information, making detection challenging without specific network and process monitoring. The technique relies on the browser's ability to render web content and dump its Document Object Model, which can be leveraged to retrieve various file types.

Attack Chain

1. An attacker's tool or script executes a Chromium-based web browser (e.g., chrome.exe, msedge.exe, brave.exe, opera.exe, vivaldi.exe) on a compromised endpoint.
2. The browser is launched with specific command-line arguments, including --headless, indicating it should run without a visible user interface.
3. The --dump-dom command-line argument is supplied to the browser, instructing it to render a specified URL and output its Document Object Model, which can be used to capture or retrieve content.
4. The headless browser initiates an outbound network connection to a specified malicious URL or a suspicious file-sharing domain (e.g., anonfiles.com, cdn.discordapp.com, githubusercontent.com).
5. The browser stealthily downloads content from the remote server, which may include malware, additional stage tools, or files for exfiltration.
6. The downloaded content is then utilized for subsequent phases of the DUCKTAIL campaign, such as credential harvesting, data exfiltration, or further system compromise.

Impact

Successful exploitation allows attackers, such as DUCKTAIL, to download additional malicious payloads, maintain persistence, exfiltrate sensitive data, or install infostealers. The stealthy nature of this technique makes it difficult for users to detect, potentially leading to prolonged compromise and significant data breaches. DUCKTAIL campaigns have historically targeted individuals and businesses, primarily focusing on information theft, especially credentials for social media and business platforms, leading to financial fraud and intellectual property theft.

Recommendation

• Deploy the Sigma rule provided in this brief to your SIEM and tune for your environment to detect suspicious headless browser activity.
• Ensure Cisco Network Visibility Module logs are collected and ingested into your SIEM platform to facilitate detection based on network flow data.
• Implement network egress filtering to block connections to the suspicious file-sharing domains listed in the IOC table.
• Monitor process creation and command-line arguments for browser executables to identify --headless and --dump-dom usage from unexpected processes or user contexts.