Detect Microsoft SharePoint Deserialization of Untrusted Data (CVE-2026-20963) in Google Chronicle
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
YARA-L Detection Query
rule sharepoint_deserialization_child_process_cve_2026_20963 {
meta:
author = "df00tech"
description = "Detects SharePoint w3wp.exe spawning suspicious child processes - CVE-2026-20963"
severity = "CRITICAL"
priority = "HIGH"
events:
$proc.metadata.event_type = "PROCESS_LAUNCH"
$proc.principal.process.file.full_path = /w3wp\.exe$/i
$proc.target.process.file.full_path = /(powershell|cmd|wscript|cscript|mshta|certutil|bitsadmin|regsvr32)\.exe$/i
condition:
$proc
}Chronicle YARA-L rule detecting SharePoint IIS worker processes spawning known living-off-the-land binaries, consistent with CVE-2026-20963 deserialization exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate SharePoint administrative cmdlets invoked via automation frameworks
- Security software performing process injection detection under IIS context
- SharePoint on-premises patching pipelines using PowerShell
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
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