Potentially Suspicious Regsvr32 HTTP/FTP Pattern

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

Detects regsvr32 execution to download/install/register new DLLs that are hosted on Web or FTP servers.

MITRE ATT&CK coverage

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

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: Potentially Suspicious Regsvr32 HTTP/FTP Pattern
id: 867356ee-9352-41c9-a8f2-1be690d78216
related:
    - id: 8e2b24c9-4add-46a0-b4bb-0057b4e6187d
      type: obsolete
status: test
description: Detects regsvr32 execution to download/install/register new DLLs that are hosted on Web or FTP servers.
references:
    - https://twitter.com/mrd0x/status/1461041276514623491
    - https://twitter.com/tccontre18/status/1480950986650832903
    - https://lolbas-project.github.io/lolbas/Binaries/Regsvr32/
author: Florian Roth (Nextron Systems)
date: 2023-05-24
modified: 2023-05-26
tags:
    - attack.stealth
    - attack.t1218.010
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\regsvr32.exe'
        - OriginalFileName: 'REGSVR32.EXE'
    selection_flag:
        CommandLine|contains:
            - ' /i'
            - ' -i'
    selection_protocol:
        CommandLine|contains:
            - 'ftp'
            - 'http'
    condition: all of selection_*
falsepositives:
    - Unknown
level: medium

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_flag`

selection_flag:
    CommandLine|contains:
        - ' /i'
        - ' -i'

Stage 3: `selection_protocol`

selection_protocol:
    CommandLine|contains:
        - 'ftp'
        - 'http'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`-i` `/i` corpus 2 (sigma 2) `ftp` corpus 6 (elastic 4, sigma 2) `http` corpus 52 (sigma 34, elastic 15, chronicle 2, splunk 1)	`field:"CommandLine" kind:match`
`Image`	ends_with	`\regsvr32.exe` corpus 64 (sigma 64)	`field:"Image" kind:ends_with value:"\regsvr32.exe"`
`OriginalFileName`	eq	`REGSVR32.EXE` corpus 37 (sigma 17, elastic 15, splunk 5)	`field:"OriginalFileName" kind:eq value:"REGSVR32.EXE"`

Potentially Suspicious Regsvr32 HTTP/FTP Pattern

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_img

Stage 2: selection_flag

Stage 3: selection_protocol

Indicators

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_flag`

Stage 3: `selection_protocol`