Process Memory Dump Via Comsvcs.DLL

Status: test
Severity: high
Log source: product windows, category process_creation
Author: Florian Roth (Nextron Systems), Modexp, Nasreddine Bencherchali (Nextron Systems), Swachchhanda Shrawan Poudel (Nextron Systems)
Source: github.com/SigmaHQ/sigma

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

MITRE ATT&CK coverage

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

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation

Rule body yaml

title: Process Memory Dump Via Comsvcs.DLL
id: 646ea171-dded-4578-8a4d-65e9822892e3
related:
    - id: 09e6d5c0-05b8-4ff8-9eeb-043046ec774c
      type: obsolete
status: test
description: Detects a process memory dump via "comsvcs.dll" using rundll32, covering multiple different techniques (ordinal, minidump function, etc.)
references:
    - https://twitter.com/shantanukhande/status/1229348874298388484
    - https://twitter.com/pythonresponder/status/1385064506049630211?s=21
    - https://twitter.com/Hexacorn/status/1224848930795552769
    - https://modexp.wordpress.com/2019/08/30/minidumpwritedump-via-com-services-dll/
    - https://twitter.com/SBousseaden/status/1167417096374050817
    - https://twitter.com/Wietze/status/1542107456507203586
    - https://github.com/Hackndo/lsassy/blob/14d8f8ae596ecf22b449bfe919829173b8a07635/lsassy/dumpmethod/comsvcs.py
    - https://www.youtube.com/watch?v=52tAmVLg1KM&t=2070s
author: Florian Roth (Nextron Systems), Modexp, Nasreddine Bencherchali (Nextron Systems), Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2020-02-18
modified: 2025-02-23
tags:
    - attack.credential-access
    - attack.stealth
    - attack.t1036
    - attack.t1003.001
    - car.2013-05-009
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\rundll32.exe'
        - OriginalFileName: 'RUNDLL32.EXE'
        - CommandLine|contains: 'rundll32'
    selection_cli_1:
        CommandLine|contains|all:
            - 'comsvcs'
            - 'full'
        CommandLine|contains:
            - '#-'
            - '#+'
            - '#24'
            - '24 '
            - 'MiniDump' # Matches MiniDump and MinidumpW
            - '#65560' # ordinal is 16 bit ordinal, so if you make the number large enough (don't fit in 16 bit space), then it normally wraps around.  for e.g ordinal 24 can be also represented by 65560 (65536+24)
    selection_generic:
        CommandLine|contains|all:
            - '24'
            - 'comsvcs'
            - 'full'
        CommandLine|contains:
            - ' #'
            - ',#'
            - ', #'
            - '"#'
    condition: (selection_img and 1 of selection_cli_*) or selection_generic
falsepositives:
    - Unlikely
level: high

Stages and Predicates

Stage 0: `condition`

(selection_img and 1 of selection_cli_*) or selection_generic

Stage 1: `selection_img`

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

Stage 2: `selection_cli_1`

selection_cli_1:
    CommandLine|contains|all:
        - 'comsvcs'
        - 'full'
    CommandLine|contains:
        - '#-'
        - '#+'
        - '#24'
        - '24 '
        - 'MiniDump'
        - '#65560'

Stage 3: `selection_generic`

selection_generic:
    CommandLine|contains|all:
        - '24'
        - 'comsvcs'
        - 'full'
    CommandLine|contains:
        - ' #'
        - ',#'
        - ', #'
        - '"#'

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 2 (sigma 1, chronicle 1) `"#` `#+` corpus 4 (sigma 3, chronicle 1) `#-` corpus 4 (sigma 3, chronicle 1) `#24` corpus 2 (sigma 1, chronicle 1) `#65560` `, #` corpus 3 (sigma 2, chronicle 1) `,#` corpus 3 (sigma 2, chronicle 1) `24` corpus 2 (sigma 1, chronicle 1) `24` `MiniDump` corpus 5 (sigma 4, chronicle 1) `comsvcs` corpus 3 (sigma 2, chronicle 1) `full` corpus 3 (sigma 2, chronicle 1) `rundll32` corpus 26 (sigma 23, chronicle 2, kusto 1)
`Image`	ends_with	`\rundll32.exe` corpus 95 (sigma 95)
`OriginalFileName`	eq	`RUNDLL32.EXE` corpus 62 (sigma 35, splunk 21, elastic 6)

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Process Memory Dump Via Comsvcs.DLL

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cli_1`

Stage 3: `selection_generic`

Indicators

Keyboard shortcuts

Search operators

Process Memory Dump Via Comsvcs.DLL

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_img

Stage 2: selection_cli_1

Stage 3: selection_generic

Indicators

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cli_1`

Stage 3: `selection_generic`