UAC Bypass Using NTFS Reparse Point - Process

Severity: high
Author: Christian Burkard (Nextron Systems)
Source: upstream

Detects the pattern of UAC Bypass using NTFS reparse point and wusa.exe DLL hijacking (UACMe 36)

MITRE ATT&CK coverage

Tactic	Techniques
Privilege Escalation	`T1548.002` Abuse Elevation Control Mechanism: Bypass User Account Control
Defense Evasion	`T1548.002` Abuse Elevation Control Mechanism: Bypass User Account Control

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `1 of selection1`

IntegrityLevel: [High, S-1-16-12288, S-1-16-16384, System]
CommandLine|endswith: '\AppData\Local\Temp\update.msu'
CommandLine|startswith: '"C:\Windows\system32\wusa.exe"  /quiet C:\Users\'

Stage 2: `1 of selection2`

IntegrityLevel: [High, System]
CommandLine|contains: 'C:\Users\'
CommandLine|contains: '\AppData\Local\Temp\'
CommandLine|contains: '\dismhost.exe {'
Image|endswith: '\DismHost.exe'
ParentCommandLine: '"C:\Windows\system32\dism.exe" /online /quiet /norestart /add-package /packagepath:"C:\Windows\system32\pe386" /ignorecheck'

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	`\AppData\Local\Temp\update.msu`
`CommandLine`	match	`C:\Users\` corpus 5 (sigma 5) `\AppData\Local\Temp\` corpus 16 (sigma 16) `\dismhost.exe {` corpus 2 (sigma 2)
`CommandLine`	starts_with	`"C:\Windows\system32\wusa.exe" /quiet C:\Users\`
`Image`	ends_with	`\DismHost.exe` corpus 2 (sigma 2)
`IntegrityLevel`	eq	`High` corpus 16 (sigma 16) `S-1-16-12288` corpus 16 (sigma 16) `S-1-16-16384` corpus 21 (sigma 21) `System` corpus 21 (sigma 21)
`ParentCommandLine`	eq	`"C:\Windows\system32\dism.exe" /online /quiet /norestart /add-package /packagepath:"C:\Windows\system32\pe386" /ignorecheck`