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Detection rules › Sigma

Suspicious Chromium Browser Instance Executed With Custom Extension

Severity
high
Author
Aedan Russell, frack113, X__Junior (Nextron Systems)
Source
upstream

Detects a suspicious process spawning a Chromium based browser process with the 'load-extension' flag to start an instance with a custom extension

MITRE ATT&CK coverage

TacticTechniques
PersistenceT1176.001 Software Extensions: Browser Extensions

Event coverage

ProviderEvent IDTitle
Sysmon1Process creation
Security-Auditing4688A new process has been created.

Stages and Predicates

Stage 1: selection

or:
Image|endswith: '\brave.exe'
Image|endswith: '\chrome.exe'
Image|endswith: '\msedge.exe'
Image|endswith: '\opera.exe'
Image|endswith: '\vivaldi.exe'
or:
ParentImage|endswith: '\cmd.exe'
ParentImage|endswith: '\cscript.exe'
ParentImage|endswith: '\mshta.exe'
ParentImage|endswith: '\powershell.exe'
ParentImage|endswith: '\pwsh.exe'
ParentImage|endswith: '\regsvr32.exe'
ParentImage|endswith: '\rundll32.exe'
ParentImage|endswith: '\wscript.exe'
CommandLine|contains: '--load-extension='

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.

FieldKindValues
CommandLinematch
  • --load-extension= corpus 2 (sigma 2)
Imageends_with
  • \brave.exe corpus 20 (sigma 20)
  • \chrome.exe corpus 11 (sigma 11)
  • \msedge.exe corpus 22 (sigma 22)
  • \opera.exe corpus 21 (sigma 21)
  • \vivaldi.exe corpus 19 (sigma 19)
ParentImageends_with
  • \cmd.exe corpus 13 (sigma 13)
  • \cscript.exe corpus 14 (sigma 14)
  • \mshta.exe corpus 10 (sigma 10)
  • \powershell.exe corpus 16 (sigma 16)
  • \pwsh.exe corpus 16 (sigma 16)
  • \regsvr32.exe corpus 11 (sigma 11)
  • \rundll32.exe corpus 12 (sigma 12)
  • \wscript.exe corpus 14 (sigma 14)

Neighbors

Broader alternatives (more inclusive than this rule)

These rules match a superset of what this rule catches. They cover the same events plus more. Use them if you want wider coverage and can absorb more false positives.