cxpid Identifying Strings

Hunt Hypothesis

The cxpid Identifying Strings rule detects potential adversary attempts to identify or exfiltrate sensitive data through string analysis, which may indicate reconnaissance or data extraction activities. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify early-stage threats and prevent data compromise.

YARA Rule

rule cxpidStrings
{
    meta:
        description = "cxpid Identifying Strings"
        author = "Seth Hardy"
        last_modified = "2014-06-23"
        
    strings:
        $ = "/cxpid/submit.php?SessionID="
        $ = "/cxgid/"
        $ = "E21BC52BEA2FEF26D005CF"
        $ = "E21BC52BEA39E435C40CD8"
        $ = "                   -,L-,O+,Q-,R-,Y-,S-"
        
    condition:
       any of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints
• Source Rule

False Positive Guidance

• Scenario: Scheduled Backup Job Using cxpid in Log Files
  Description: A backup tool or script logs the cxpid string as part of its operation, such as during a database dump or file transfer.
  Filter/Exclusion: process.name != "backup_tool.exe" OR event_id != "backup_log"

• Scenario: System Administration Task Using cxpid in Command Line
  Description: An admin runs a command-line tool (e.g., cxpid.exe) for system diagnostics or configuration, which includes the string in its output.
  Filter/Exclusion: process.name != "cxpid.exe" OR user.name != "admin"

• Scenario: Log File Rotation or Purge Process
  Description: A log management tool (e.g., Splunk, ELK Stack) rotates or purges logs, and the cxpid string appears in the log entries as part of the process.
  Filter/Exclusion: process.name != "logrotate.exe" OR event_id != "log_rotation"

• Scenario: Application Using cxpid in Debug Output
  Description: A legitimate application (e.g., custom CRM or ERP system) logs cxpid as part of its internal debugging or session tracking.
  Filter/Exclusion: process.name != "crm_app.exe" OR log_level != "debug"

• Scenario: Network Monitoring Tool Generating cxpid in Traffic Logs
  Description: A network monitoring tool (e.g., Wireshark, PRTG) logs cxpid as part of packet analysis or traffic classification.
  Filter/Exclusion: process.name != "wireshark.exe" OR event_id != "network_traffic"