Identifies the desktopimgdownldr utility being used to download a remote file. An adversary may use desktopimgdownldr to download arbitrary files as an alternative to certutil.
Rule type: eql
Risk score: 47
Runs every: 5m
Maximum alerts per execution: 100
- Threat Detection
- Command and Control
Rule license: Elastic License v2
## Triage and analysis ### Investigating Remote File Download via Desktopimgdownldr Utility Attackers commonly transfer tooling or malware from external systems into a compromised environment using the command and control channel. However, they can also abuse signed utilities to drop these files. The `Desktopimgdownldr.exe` utility is used to to configure lockscreen/desktop image, and can be abused with the `lockscreenurl` argument to download remote files and tools, this rule looks for this behavior. #### Possible investigation steps - Investigate the process execution chain (parent process tree). - Identify the user account that performed the action and whether it should perform this kind of action. - Contact the account owner and confirm whether they are aware of this activity. - Investigate other alerts associated with the user/host during the past 48 hours. - Determine if the activity is unique by validating if other machines in the organization have similar entries. - Check the reputation of the domain or IP address used to host the downloaded file or if the user downloaded the file from an internal system. - Retrieve the file and determine if it is malicious: - Identify the file type. - Use a private sandboxed malware analysis system to perform analysis. - Observe and collect information about the following activities: - Attempts to contact external domains and addresses. - File and registry access, modification, and creation activities. - Service creation and launch activities. - Scheduled tasks creation. - Use the PowerShell Get-FileHash cmdlet to get the SHA-256 hash value of the file. - Search for the existence and reputation of this file in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc. ### False positive analysis - This activity is unusual but can be done by administrators. Benign true positives (B-TPs) can be added as exceptions if necessary. - Analysts can dismiss the alert if the downloaded file is a legitimate image. ### Response and remediation - Initiate the incident response process based on the outcome of the triage. - Isolate the involved host to prevent further post-compromise behavior. - If the triage identified malware, search the environment for additional compromised hosts. - Implement any temporary network rules, procedures, and segmentation required to contain the malware. - Immediately block the IoCs identified. - Remove and block malicious artifacts identified on the triage. - Disable the involved accounts, or restrict their ability to log on remotely. - Reset passwords for the user account and other potentially compromised accounts (email, services, CRMs, etc.). - Investigate the initial attack vector. ## Config If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define `event.ingested` and default fallback for EQL rules was not added until 8.2, so you will need to add a custom pipeline to populate `event.ingested` to @timestamp for this rule to work.
process where event.type in ("start", "process_started") and (process.name : "desktopimgdownldr.exe" or process.pe.original_file_name == "desktopimgdownldr.exe") and process.args : "/lockscreenurl:http*"
Framework: MITRE ATT&CKTM