IMPORTANT: No additional bug fixes or documentation updates
will be released for this version. For the latest information, see the
current release documentation.
Remote File Download via Desktopimgdownldr Utility
editRemote File Download via Desktopimgdownldr Utility
editIdentifies 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
Rule indices:
- winlogbeat-*
- logs-endpoint.events.*
- logs-windows.*
Severity: medium
Risk score: 47
Runs every: 5m
Searches indices from: now-9m (Date Math format, see also Additional look-back time
)
Maximum alerts per execution: 100
References:
Tags:
- Elastic
- Host
- Windows
- Threat Detection
- Command and Control
Version: 6
Rule authors:
- Elastic
Rule license: Elastic License v2
Investigation guide
edit## 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.
Rule query
editprocess 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
-
Tactic:
- Name: Command and Control
- ID: TA0011
- Reference URL: https://attack.mitre.org/tactics/TA0011/
-
Technique:
- Name: Ingress Tool Transfer
- ID: T1105
- Reference URL: https://attack.mitre.org/techniques/T1105/