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Detection rules › Sigma

Suspicious Desktopimgdownldr Target File

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

Detects a suspicious Microsoft desktopimgdownldr file creation that stores a file to a suspicious location or contains a file with a suspicious extension

MITRE ATT&CK coverage

TacticTechniques
Command & ControlT1105 Ingress Tool Transfer

Event coverage

ProviderEventTitle
SysmonEvent ID 11FileCreate

Rule body yaml

title: Suspicious Desktopimgdownldr Target File
id: fc4f4817-0c53-4683-a4ee-b17a64bc1039
status: test
description: Detects a suspicious Microsoft desktopimgdownldr file creation that stores a file to a suspicious location or contains a file with a suspicious extension
references:
    - https://labs.sentinelone.com/living-off-windows-land-a-new-native-file-downldr/
    - https://twitter.com/SBousseaden/status/1278977301745741825
author: Florian Roth (Nextron Systems)
date: 2020-07-03
modified: 2022-06-02
tags:
    - attack.command-and-control
    - attack.t1105
logsource:
    product: windows
    category: file_event
detection:
    selection:
        Image|endswith: '\svchost.exe'
        TargetFilename|contains: '\Personalization\LockScreenImage\'
    filter1:
        TargetFilename|contains: 'C:\Windows\'
    filter2:
        TargetFilename|contains:
            - '.jpg'
            - '.jpeg'
            - '.png'
    condition: selection and not filter1 and not filter2
falsepositives:
    - False positives depend on scripts and administrative tools used in the monitored environment
level: high

Stages and Predicates

Stage 0: condition

selection and not filter1 and not filter2

Stage 1: selection

selection:
    Image|endswith: '\svchost.exe'
    TargetFilename|contains: '\Personalization\LockScreenImage\'

Stage 2: not filter1

filter1:
    TargetFilename|contains: 'C:\Windows\'

Stage 3: not filter2

filter2:
    TargetFilename|contains:
        - '.jpg'
        - '.jpeg'
        - '.png'

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

FieldKindExcluded values
TargetFilenamematchC:\Windows\
TargetFilenamematch.jpeg
TargetFilenamematch.jpg
TargetFilenamematch.png

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
Imageends_with
  • \svchost.exe corpus 23 (sigma 23)
TargetFilenamematch
  • \Personalization\LockScreenImage\