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Potential Privilege Escalation Using Symlink Between Osk and Cmd

Status
test
Severity
high
Log source
product windows, category process_creation
Author
frack113
Source
github.com/SigmaHQ/sigma

Detects the creation of a symbolic link between "cmd.exe" and the accessibility on-screen keyboard binary (osk.exe) using "mklink". This technique provides an elevated command prompt to the user from the login screen without the need to log in.

MITRE ATT&CK coverage

TacticTechniques
PersistenceT1546.008 Event Triggered Execution: Accessibility Features
Privilege EscalationT1546.008 Event Triggered Execution: Accessibility Features

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation

Rule body yaml

title: Potential Privilege Escalation Using Symlink Between Osk and Cmd
id: e9b61244-893f-427c-b287-3e708f321c6b
status: test
description: Detects the creation of a symbolic link between "cmd.exe" and the accessibility on-screen keyboard binary (osk.exe) using "mklink". This technique provides an elevated command prompt to the user from the login screen without the need to log in.
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/5c1e6f1b4fafd01c8d1ece85f510160fc1275fbf/atomics/T1546.008/T1546.008.md
    - https://ss64.com/nt/mklink.html
author: frack113
date: 2022-12-11
modified: 2022-12-20
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.t1546.008
logsource:
    product: windows
    category: process_creation
detection:
    selection_img:
        - Image|endswith: '\cmd.exe'
        - OriginalFileName: 'Cmd.Exe'
    selection_cli:
        CommandLine|contains|all:
            - 'mklink'
            - '\osk.exe'
            - '\cmd.exe'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_cmd_mklink_osk_cmd/info.yml

Stages and Predicates

Stage 0: condition

all of selection_*

Stage 1: selection_img

selection_img:
    - Image|endswith: '\cmd.exe'
    - OriginalFileName: 'Cmd.Exe'

Stage 2: selection_cli

selection_cli:
    CommandLine|contains|all:
        - 'mklink'
        - '\osk.exe'
        - '\cmd.exe'

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
  • \cmd.exe
  • \osk.exe
  • mklink corpus 3 (sigma 2, splunk 1)
Imageends_with
  • \cmd.exe corpus 130 (sigma 130)
OriginalFileNameeq
  • Cmd.Exe corpus 65 (sigma 43, splunk 17, elastic 5)