Detect Microsoft Office Word Reliance on Untrusted Inputs in Security Decision (CVE-2026-21514) in Sumo Logic CSE
Detects exploitation of CVE-2026-21514, a Microsoft Office Word vulnerability classified as CWE-807 (Reliance on Untrusted Inputs in a Security Decision). This flaw allows attackers to manipulate security-relevant decisions in Word by supplying crafted untrusted input, potentially bypassing security controls such as Protected View, macro policy enforcement, or document trust decisions. This CVE is listed on the CISA KEV catalog, indicating active exploitation in the wild.
MITRE ATT&CK
Sumo Detection Query
_sourceCategory=windows/sysmon EventID=1
| parse field=Message "ParentImage: *\n" as parent_image
| parse field=Message "Image: *\n" as child_image
| parse field=Message "CommandLine: *\n" as command_line
| parse field=Message "User: *\n" as user
| where parent_image matches "*WINWORD.EXE"
| where child_image matches "*cmd.exe" or child_image matches "*powershell.exe" or child_image matches "*wscript.exe" or child_image matches "*cscript.exe" or child_image matches "*mshta.exe" or child_image matches "*rundll32.exe" or child_image matches "*regsvr32.exe" or child_image matches "*certutil.exe" or child_image matches "*bitsadmin.exe"
| count by _sourceHost, user, parent_image, child_image, command_line
| sort by _count descSumo Logic query parsing Sysmon Event ID 1 process creation logs to identify WINWORD.EXE spawning suspicious child processes, aggregated by host and user for triage.
Data Sources
False Positives & Tuning
- Approved business automation workflows using Word macros with system utility invocations
- IT provisioning scripts that open Word documents and trigger helper process execution
- Word-based testing harnesses in development environments
- Legitimate document conversion pipelines that use cmd to invoke Word and post-process output
Other platforms for CVE-2026-21514
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 1Word Spawns PowerShell via Macro — Security Bypass Simulation
Expected signal: Sysmon Event ID 1 showing WINWORD.EXE as ParentImage with powershell.exe as child Image; PowerShell ScriptBlock logging Event ID 4104; network telemetry if payload attempts outbound connection
- Test 2Word Drops Executable to Temp via Macro
Expected signal: Sysmon Event ID 11 (FileCreate) with Image=WINWORD.EXE and TargetFilename ending in .exe under %TEMP%; DeviceFileEvents in MDE showing InitiatingProcessFileName=WINWORD.EXE
- Test 3Word Initiates External Network Connection via mshta Child Process
Expected signal: Sysmon Event ID 1 with ParentImage=WINWORD.EXE and Image=mshta.exe; subsequent cmd.exe spawn from mshta.exe visible in process tree; file creation in TEMP
- Test 4Mark-of-the-Web Bypass Check — Simulated Internet-Origin Document Open
Expected signal: Sysmon Event ID 15 (FileCreateStreamHash) capturing Zone.Identifier ADS creation and deletion; Windows Defender SmartScreen or Office MOTW telemetry in event logs
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