Detect CVE-2026-21510: Microsoft Windows Shell Protection Mechanism Failure in Sumo Logic CSE
Detects exploitation of CVE-2026-21510, a Microsoft Windows Shell protection mechanism failure (CWE-693) that allows attackers to bypass security controls enforced by the Windows Shell. This vulnerability is actively exploited in the wild (CISA KEV). Attackers may abuse this flaw to execute unauthorized code, bypass security prompts, or escalate privileges via crafted shell interactions.
MITRE ATT&CK
Sumo Detection Query
_sourceCategory=windows/sysmon (EventCode=1)
| parse "<Image>*</Image>" as process_image
| parse "<ParentImage>*</ParentImage>" as parent_image
| parse "<CommandLine>*</CommandLine>" as command_line
| parse "<ParentCommandLine>*</ParentCommandLine>" as parent_cmd
| parse "<User>*</User>" as username
| parse "<UtcTime>*</UtcTime>" as event_time
| eval process_name = toUpperCase(substring(process_image, length(process_image) - indexOf(reverse(process_image), "\\") + 1))
| eval parent_name = toUpperCase(substring(parent_image, length(parent_image) - indexOf(reverse(parent_image), "\\") + 1))
| where (parent_name in ("WINLOGON.EXE", "SERVICES.EXE", "SVCHOST.EXE", "LSASS.EXE", "CSRSS.EXE") and process_name in ("EXPLORER.EXE", "CMD.EXE", "POWERSHELL.EXE", "PWSH.EXE", "WSCRIPT.EXE", "CSCRIPT.EXE", "MSHTA.EXE"))
or (process_name = "EXPLORER.EXE" and (matches(command_line, "(?i).*\/factory.*") or matches(command_line, "(?i).*-Embedding.*")) and parent_name != "USERINIT.EXE")
| count by _sourceHost, username, parent_name, process_name, command_line
| sort by _count descSumo Logic query on Sysmon process creation events to detect Windows Shell protection bypass patterns. Identifies shell processes launched from unexpected system-level parents and abnormal explorer.exe instantiation methods associated with CVE-2026-21510.
Data Sources
Required Tables
False Positives & Tuning
- Endpoint management solutions (e.g., Tanium, BigFix) that invoke shell processes from service contexts
- Legitimate COM-based shell extension activation using /factory or -Embedding flags
- Automated patch management scripts executed in service account context spawning cmd.exe
- Developer workstations running build automation that invokes shell from background services
Other platforms for CVE-2026-21510
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Simulate Shell Spawn from Winlogon Context
Expected signal: Sysmon Event ID 1: cmd.exe process with ParentImage path containing winlogon.exe or SYSTEM session identifier; Windows Security Event 4688 showing cmd.exe process creation under SYSTEM account.
- Test 2Explorer.exe Factory Flag Instantiation
Expected signal: Sysmon Event ID 1: explorer.exe process with CommandLine containing /factory and ParentImage of powershell.exe; corresponding network or registry activity from the new explorer instance.
- Test 3PowerShell Encoded Command via Shell Bypass Chain
Expected signal: Sysmon Event ID 1: powershell.exe with -EncodedCommand in CommandLine, parent cmd.exe; Sysmon Event ID 3: any outbound connection if payload includes network activity.
- Test 4Shell Bypass Followed by Discovery Commands
Expected signal: Sysmon Event IDs 1 for cmd.exe (parent: psexec/SYSTEM), then whoami.exe and ipconfig.exe as children within 30 seconds; all events share the same host identifier.
Unlock Pro Content
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