Regsvr32 DLL Execution With Suspicious File Extension

Status: test
Severity: high
Log source: product windows, category process_creation
Author: Florian Roth (Nextron Systems), frack113
Source: github.com/SigmaHQ/sigma

Detects the execution of REGSVR32.exe with DLL files masquerading as other files

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218.010` System Binary Proxy Execution: Regsvr32

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation

Rule body yaml

title: Regsvr32 DLL Execution With Suspicious File Extension
id: 089fc3d2-71e8-4763-a8a5-c97fbb0a403e
related:
    - id: 8e2b24c9-4add-46a0-b4bb-0057b4e6187d
      type: obsolete
status: test
description: Detects the execution of REGSVR32.exe with DLL files masquerading as other files
references:
    - https://thedfirreport.com/2021/11/29/continuing-the-bazar-ransomware-story/
    - https://blog.talosintelligence.com/2021/10/threat-hunting-in-large-datasets-by.html
    - https://guides.lib.umich.edu/c.php?g=282942&p=1885348
    - https://harfanglab.io/insidethelab/uac-0057-pressure-ukraine-poland/
author: Florian Roth (Nextron Systems), frack113
date: 2021-11-29
modified: 2025-08-27
tags:
    - attack.stealth
    - attack.t1218.010
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\regsvr32.exe'
        - OriginalFileName: 'REGSVR32.EXE'
    selection_cli:
        CommandLine|endswith:
            # Add more image extensions
            # https://twitter.com/Max_Mal_/status/1542461200797163522/photo/3
            - '.bin'
            - '.bmp'
            - '.cr2'
            - '.dat'
            - '.eps'
            - '.gif'
            - '.ico'
            - '.jpeg'
            - '.jpg'
            - '.log'
            - '.nef'
            - '.orf'
            - '.png'
            - '.raw'
            - '.rtf'
            - '.sr2'
            - '.temp'
            - '.tif'
            - '.tiff'
            - '.tmp'
            - '.txt'
    condition: all of selection_*
falsepositives:
    - Unlikely
level: high

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith: '\regsvr32.exe'
    - OriginalFileName: 'REGSVR32.EXE'

Stage 2: `selection_cli`

selection_cli:
    CommandLine|endswith:
        - '.bin'
        - '.bmp'
        - '.cr2'
        - '.dat'
        - '.eps'
        - '.gif'
        - '.ico'
        - '.jpeg'
        - '.jpg'
        - '.log'
        - '.nef'
        - '.orf'
        - '.png'
        - '.raw'
        - '.rtf'
        - '.sr2'
        - '.temp'
        - '.tif'
        - '.tiff'
        - '.tmp'
        - '.txt'

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`	ends_with	`.bin` `.bmp` `.cr2` `.dat` corpus 6 (sigma 6) `.eps` `.gif` corpus 3 (sigma 3) `.ico` `.jpeg` corpus 3 (sigma 3) `.jpg` corpus 2 (sigma 2) `.log` corpus 2 (sigma 2) `.nef` `.orf` `.png` corpus 3 (sigma 3) `.raw` `.rtf` `.sr2` `.temp` corpus 2 (sigma 2) `.tif` `.tiff` `.tmp` corpus 2 (sigma 2) `.txt` corpus 4 (sigma 4)
`Image`	ends_with	`\regsvr32.exe` corpus 65 (sigma 65)
`OriginalFileName`	eq	`REGSVR32.EXE` corpus 26 (sigma 17, splunk 6, elastic 3)

`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)

Regsvr32 DLL Execution With Suspicious File Extension

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cli`

Indicators

Keyboard shortcuts

Search operators

Regsvr32 DLL Execution With Suspicious File Extension

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_img

Stage 2: selection_cli

Indicators

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cli`