Agent Skills: Detecting T1548 Abuse Elevation Control Mechanism

Detecting T1548 Abuse Elevation Control Mechanism

When to Use

• When hunting for privilege escalation via UAC bypass in Windows environments
• After threat intelligence indicates use of UAC bypass exploits by active threat groups
• When investigating how attackers achieved administrative access without triggering UAC prompts
• During security assessments to validate UAC bypass detection coverage
• When monitoring for setuid/setgid abuse on Linux systems

Prerequisites

• Sysmon Event ID 1 with command-line and parent process logging
• Windows Security Event ID 4688 with process tracking
• Registry auditing for UAC-related keys (HKCU\Software\Classes)
• Sysmon Event ID 12/13 (Registry key/value modification)
• EDR with elevation monitoring capabilities

Workflow

1. Monitor UAC Registry Modifications: Many UAC bypasses modify registry keys under HKCU\Software\Classes\ms-settings\shell\open\command or HKCU\Software\Classes\mscfile\shell\open\command. Track Sysmon Events 12/13 for these changes.
2. Detect Auto-Elevating Process Abuse: Certain Windows binaries auto-elevate without UAC prompts (fodhelper.exe, computerdefaults.exe, eventvwr.exe). Hunt for these being launched by non-standard parent processes.
3. Track Process Integrity Level Changes: Monitor for processes escalating from medium to high integrity level without corresponding UAC consent events.
4. Hunt for Elevated Process Spawning: Detect when auto-elevating processes spawn unexpected children (cmd.exe, powershell.exe) -- indicating UAC bypass exploitation.
5. Monitor Linux Elevation Abuse: Track sudo misconfiguration exploitation, setuid binary abuse, and capability manipulation.
6. Correlate with Privilege Escalation Chain: Map elevation abuse to the broader attack chain, identifying what was done with escalated privileges.

Key Concepts

| Concept | Description | |---------|-------------| | T1548.002 | Bypass User Account Control | | T1548.001 | Setuid and Setgid (Linux) | | T1548.003 | Sudo and Sudo Caching | | T1548.004 | Elevated Execution with Prompt (macOS) | | UAC Auto-Elevation | Windows binaries that elevate without prompt | | fodhelper.exe | Common UAC bypass vector via registry hijack | | eventvwr.exe | MSC file handler UAC bypass | | Integrity Level | Windows process trust level (Low/Medium/High/System) |

Detection Queries

Splunk -- UAC Bypass via Registry Modification

index=sysmon (EventCode=12 OR EventCode=13)
| where match(TargetObject, "(?i)HKCU\\\\Software\\\\Classes\\\\(ms-settings|mscfile|exefile|Folder)\\\\shell\\\\open\\\\command")
| table _time Computer User EventCode TargetObject Details Image

Splunk -- Auto-Elevating Process Abuse

index=sysmon EventCode=1
| where match(Image, "(?i)(fodhelper|computerdefaults|eventvwr|sdclt|slui|cmstp)\.exe$")
| where NOT match(ParentImage, "(?i)(explorer|svchost|services)\.exe$")
| table _time Computer User Image CommandLine ParentImage ParentCommandLine

KQL -- UAC Bypass Detection

DeviceRegistryEvents
| where Timestamp > ago(7d)
| where RegistryKey has_any ("ms-settings\\shell\\open\\command", "mscfile\\shell\\open\\command")
| where ActionType == "RegistryValueSet"
| project Timestamp, DeviceName, RegistryKey, RegistryValueData, InitiatingProcessFileName

Sigma Rule

title: UAC Bypass via Registry Modification
status: stable
logsource:
    product: windows
    category: registry_set
detection:
    selection:
        TargetObject|contains:
            - '\ms-settings\shell\open\command'
            - '\mscfile\shell\open\command'
            - '\exefile\shell\open\command'
    condition: selection
level: high
tags:
    - attack.privilege_escalation
    - attack.t1548.002

Common Scenarios

1. fodhelper.exe Registry Hijack: Attacker sets HKCU\Software\Classes\ms-settings\shell\open\command to a malicious executable, then launches fodhelper.exe which auto-elevates and executes the hijacked command.
2. eventvwr.exe MSC Bypass: Modifying HKCU\Software\Classes\mscfile\shell\open\command to intercept Event Viewer's auto-elevation behavior.
3. sdclt.exe Bypass: Leveraging the Windows Backup utility's auto-elevation to execute arbitrary commands.
4. CMSTP.exe INF Bypass: Using Connection Manager Profile Installer with a malicious INF file to bypass UAC via /s /ni flags.
5. DLL Hijacking in Auto-Elevate: Placing malicious DLLs in search paths of auto-elevating executables.

Output Format

Hunt ID: TH-UAC-[DATE]-[SEQ]
Host: [Hostname]
Bypass Method: [Registry hijack/DLL hijack/Token manipulation]
Auto-Elevate Binary: [fodhelper.exe/eventvwr.exe/etc.]
Registry Key Modified: [Full registry path]
Payload Executed: [Command or binary path]
User Context: [Account]
Risk Level: [Critical/High/Medium]
ATT&CK Technique: [T1548.00x]