Process Memory Dump Via Comsvcs.DLL

Severity: high
Author: Florian Roth (Nextron Systems), Modexp, Nasreddine Bencherchali (Nextron Systems), Swachchhanda Shrawan Poudel (Nextron Systems)
Source: upstream

Detects a process memory dump via "comsvcs.dll" using rundll32, covering multiple different techniques (ordinal, minidump function, etc.)

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1036` Masquerading
Credential Access	`T1003.001` OS Credential Dumping: LSASS Memory

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `selection_img`

or:
CommandLine|contains: rundll32
Image|endswith: '\rundll32.exe'
OriginalFileName: RUNDLL32.EXE

Stage 2: `1 of selection_cli_1`

or:
CommandLine|contains: '#+'
CommandLine|contains: '#-'
CommandLine|contains: '#24'
CommandLine|contains: '#65560'
CommandLine|contains: '24 '
CommandLine|contains: MiniDump
CommandLine|contains: comsvcs
CommandLine|contains: full

Stage 3: `selection_generic`

or:
CommandLine|contains: ' #'
CommandLine|contains: ', #'
CommandLine|contains: ',#'
CommandLine|contains: '"#'
CommandLine|contains: 24
CommandLine|contains: comsvcs
CommandLine|contains: full

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`CommandLine`	match	`#` `"#` `#+` corpus 3 (sigma 3) `#-` corpus 3 (sigma 3) `#24` `#65560` `, #` `,#` `24` `24` `MiniDump` corpus 3 (sigma 3) `comsvcs` corpus 2 (sigma 2) `full` `rundll32` corpus 19 (sigma 19)
`Image`	ends_with	`\rundll32.exe` corpus 76 (sigma 76)
`OriginalFileName`	eq	`RUNDLL32.EXE` corpus 28 (sigma 25, splunk 3)