Adversaries may abuse BITS jobs to persistently execute or clean up after malicious payloads. Windows Background Intelligent Transfer Service (BITS) is a low-bandwidth, asynchronous file transfer mechanism exposed through Component Object Model (COM). BITS is commonly used by updaters, messengers, and other applications preferred to operate in the background (using available idle bandwidth) without interrupting other networked applications. File transfer tasks are implemented as BITS jobs, which contain a queue of one or more file operations.
Adversaries may abuse BITS to download, execute, and even clean up after running malicious code. BITS tasks are self-contained in the BITS job database, without new files or registry modifications, and often permitted by host firewalls. BITS enabled execution may also enable persistence by creating long-standing jobs (the default maximum lifetime is 90 days and extendable) or invoking an arbitrary program when a job completes or errors (including after system reboots).
|M1037||Filter Network Traffic||
Modify network and/or host firewall rules, as well as other network controls, to only allow legitimate BITS traffic.
|M1028||Operating System Configuration||
Consider reducing the default BITS job lifetime in Group Policy or by editing the
|M1018||User Account Management||
Consider limiting access to the BITS interface to specific users or groups.
BITS runs as a service and its status can be checked with the Sc query utility (
sc query bits). Active BITS tasks can be enumerated using the BITSAdmin tool (
bitsadmin /list /allusers /verbose).
Monitor usage of the BITSAdmin tool (especially the ‘Transfer’, 'Create', 'AddFile', 'SetNotifyFlags', 'SetNotifyCmdLine', 'SetMinRetryDelay', 'SetCustomHeaders', and 'Resume' command options) Admin logs, PowerShell logs, and the Windows Event log for BITS activity. Also consider investigating more detailed information about jobs by parsing the BITS job database.
Monitor and analyze network activity generated by BITS. BITS jobs use HTTP(S) and SMB for remote connections and are tethered to the creating user and will only function when that user is logged on (this rule applies even if a user attaches the job to a service account).
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