Detect CVE-2026-45659 Microsoft SharePoint Server Deserialization RCE in CrowdStrike LogScale
Detects exploitation of CVE-2026-45659, a critical deserialization of untrusted data vulnerability in Microsoft SharePoint Server. Successful exploitation allows remote code execution by sending crafted serialized .NET objects to SharePoint web endpoints. This CVE is listed in CISA KEV indicating active exploitation in the wild.
MITRE ATT&CK
- Tactic
- Initial Access Execution Persistence
LogScale Detection Query
// CVE-2026-45659 SharePoint Deserialization - Child Process from IIS Worker
#event_simpleName IN ("ProcessRollup2", "SyntheticProcessRollup2")
| ParentBaseFileName IN~ ("w3wp.exe", "owstimer.exe", "microsoft.sharepoint.exe")
| FileName IN~ ("cmd.exe", "powershell.exe", "wscript.exe", "cscript.exe", "mshta.exe", "rundll32.exe", "certutil.exe", "bitsadmin.exe", "regsvr32.exe", "msiexec.exe")
| eval suspicious_cmdline = if(match(CommandLine, "(?i)(whoami|net user|ipconfig|systeminfo|download|invoke-|iex|encodedcommand|bypass|webclient|downloadstring|base64)"), 1, 0)
| eval risk_score = case(
suspicious_cmdline = 1 AND ParentBaseFileName IN~ ("w3wp.exe"), 95,
suspicious_cmdline = 0 AND ParentBaseFileName IN~ ("w3wp.exe"), 75,
true(), 60
)
| where risk_score >= 60
| table timestamp, ComputerName, UserName, ParentBaseFileName, FileName, CommandLine, suspicious_cmdline, risk_score
| sort -risk_score, -timestampCrowdStrike Falcon CQL query detecting SharePoint deserialization exploitation by identifying suspicious child processes spawned from SharePoint IIS worker processes, with risk scoring based on command-line indicators.
Data Sources
Required Tables
False Positives & Tuning
- SharePoint health monitoring scripts that legitimately spawn cmd.exe or PowerShell for diagnostics
- Security tools running in the context of the IIS application pool that invoke system utilities for scanning
- SharePoint workflow actions or custom solutions that invoke system processes as part of business logic
Other platforms for CVE-2026-45659
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 1CVE-2026-45659 SharePoint Deserialization Simulation via ysoserial.net
Expected signal: IIS logs should show POST request to /_vti_bin/UserProfileService.asmx with large cs-bytes; Sysmon Event ID 1 should capture cmd.exe spawned by w3wp.exe with CommandLine containing whoami
- Test 2SharePoint Worker Process Suspicious Child Simulation
Expected signal: Sysmon Event ID 1 showing cmd.exe execution with Network Service account; Windows Security Event ID 4688 capturing process creation with suspicious command line arguments
- Test 3SharePoint Endpoint Fuzzing and Web Shell Upload Detection Test
Expected signal: Sysmon Event ID 11 (FileCreate) capturing .aspx file creation in SharePoint web directory path; Windows Security Event ID 4663 (file access) if object access auditing is enabled
References (4)
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45659
- https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
- https://nvd.nist.gov/vuln/detail/CVE-2026-45659
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