Detect Microsoft SharePoint Deserialization of Untrusted Data (CVE-2026-20963) in Splunk
Detects exploitation of CVE-2026-20963, a deserialization of untrusted data vulnerability in Microsoft SharePoint. Attackers can send crafted serialized payloads to SharePoint endpoints, leading to remote code execution in the context of the SharePoint application pool. This CVE is listed on the CISA KEV catalog, indicating active exploitation in the wild.
MITRE ATT&CK
- Tactic
- Initial Access Execution Persistence
SPL Detection Query
index=wineventlog OR index=sysmon sourcetype IN ("WinEventLog:Security", "XmlWinEventLog:Microsoft-Windows-Sysmon/Operational")
| eval parent=lower(ParentImage), proc=lower(Image), cmdline=lower(CommandLine)
| where (parent="*w3wp.exe*" AND proc IN ("*powershell.exe*", "*cmd.exe*", "*wscript.exe*", "*cscript.exe*", "*mshta.exe*", "*certutil.exe*"))
OR (EventCode=4688 AND parent="*w3wp.exe*" AND proc IN ("*powershell.exe*", "*cmd.exe*"))
| eval risk_reason=case(
match(proc, "powershell"), "PowerShell spawned from IIS worker",
match(proc, "certutil"), "certutil spawned from IIS worker - possible payload download",
match(proc, "mshta"), "mshta spawned from IIS worker - possible script execution",
true(), "Suspicious child process of w3wp.exe"
)
| table _time, host, parent, proc, cmdline, risk_reason
| sort -_timeDetects SharePoint IIS worker process spawning suspicious child processes on Windows hosts, which is a strong indicator of successful deserialization exploitation.
Data Sources
Required Sourcetypes
False Positives & Tuning
- SharePoint workflow activities that legitimately spawn PowerShell for data processing
- Administrative tooling running under application pool identity
- Security scanning tools executing under IIS context
Other platforms for CVE-2026-20963
Testing Methodology
Validate this detection against 3 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 SharePoint Deserialization Child Process Spawn
Expected signal: Process creation event (Event ID 4688 or Sysmon Event ID 1) with ParentImage matching w3wp_sim.exe and Image matching powershell.exe
- Test 2Craft and Submit Malformed Serialized Payload to SharePoint Endpoint
Expected signal: IIS access log entry showing POST to /_api/web/lists with non-JSON content-type or anomalous body size; WAF or SIEM alert on malformed serialized content
- Test 3Simulate Credential Dumping Post-Exploitation via w3wp.exe Context
Expected signal: Process creation event showing cmd.exe or tasklist.exe executed under SharePoint application pool identity; Event ID 4656/4663 if LSASS handle access is attempted
Unlock Pro Content
Get the full detection package for CVE-2026-20963 including response playbook, investigation guide, and atomic red team tests.