Executive Summary

• SGI detected an attempt to modify the authorized_keys file, a critical component for SSH access control.
• The activity originated from an IP address in Russia (77.50.63.xxx), indicating a potential external threat actor.
• The likely objective is to gain unauthorized remote access to systems via SSH.
• The business risk is high, potentially leading to data breaches, system compromise, and operational disruption.
• Organizations should immediately review SSH access controls and monitor for suspicious activity.

Failure to address this threat vector could lead to widespread system compromise and significant financial and reputational damage.

Observed Activity (SGI Sensors)

SGI sensors detected network activity originating from 77.50.63.250, associated with AS34602 in Moscow, Russia. The activity involved a TCP connection with a payload that, when analyzed, was identified as an attempt to inject or modify the .ssh/authorized_keys file on a target system. The payload hash was identified and checked against VirusTotal, confirming malicious intent.

Malware/Technique Overview

The observed activity indicates a credential access attempt, specifically targeting SSH keys. Attackers often attempt to modify the authorized_keys file to enable passwordless SSH login, bypassing traditional authentication mechanisms. This technique is commonly used to gain persistent access to compromised systems.

• T1078.003 – Valid Accounts: Local Accounts
• T1190 – Exploit Public-Facing Application
• T1555.004 – Credentials from Password Stores: SSH Keys
• T1059.004 – Command and Scripting Interpreter: Unix Shell
• T1021.004 – Remote Services: SSH

VirusTotal Snapshot

VirusTotal analysis showed 29 malicious detections out of 62 total scans, with 33 vendors reporting the sample as undetected. This suggests that while a significant number of security vendors recognize the threat, some remain unaware. The sample was identified under various aliases, including variations referencing redirection attempts to different user home directories. This indicates a broad, automated targeting strategy.

Some notable vendors flagged the sample as malicious.

• VirusTotal Sample

Indicators of Compromise (IoCs)

It is recommended to monitor these IoCs for at least 30 days.

Detection & Hunting

Splunk SPL

index=* src_ip=77.50.63.0/24  (file_hash=a8460f446be540410004b1a8db4083773fa46f7fe76fa84219c93daa1669f8f2 OR dest_file="*.ssh/authorized_keys")
| table _time, src_ip, dest_file, user, file_hash

This query searches for connections originating from the identified IP range and any file modifications to authorized_keys files. Review the results carefully, as legitimate administrative actions may trigger this rule. Focus on unexpected source IPs and users.

Elastic/Kibana KQL

source.ip : 77.50.63.0/24 AND (file.hash.sha256 : "a8460f446be540410004b1a8db4083773fa46f7fe76fa84219c93daa1669f8f2" OR file.path : "*/.ssh/authorized_keys")

This KQL query identifies network connections from the suspicious IP range and attempts to modify the authorized_keys file. False positives could arise from automated configuration management systems. Investigate any unusual user accounts or processes associated with these events.

Containment, Eradication & Recovery

1. Isolate Affected Systems: Immediately disconnect any systems showing signs of compromise from the network to prevent further lateral movement.
2. Block Malicious IP: Implement firewall rules to block all traffic to and from the identified malicious IP address (77.50.63.250).
3. Scan for Malware: Perform a full system scan using updated antivirus and anti-malware software on all potentially affected systems.
4. Reimage Compromised Systems: If a system is confirmed to be compromised, reimage it from a known-good backup or image.
5. Reset Credentials: Reset passwords for all user accounts on affected systems, and enforce strong password policies. Rotate SSH keys.

Inform IT and leadership of the incident. Preserve system logs and disk images for forensic analysis.

Hardening & Preventive Controls

• Multi-Factor Authentication (MFA): Enforce MFA for all SSH access (NIST CSF PR.AC-1, CIS Control 6).
• EDR Tuning: Configure Endpoint Detection and Response (EDR) solutions to detect unauthorized file modifications, especially to sensitive files like authorized_keys (NIST CSF DE.CM-7, CIS Control 10).
• Network Segmentation: Implement network segmentation to limit the blast radius of a potential compromise (NIST CSF PR.AC-4, CIS Control 14).
• Least Privilege: Apply the principle of least privilege to user accounts, limiting access to only what is necessary (NIST CSF PR.AC-3, CIS Control 5).
• Patch Management: Maintain a rigorous patch management process to address known vulnerabilities in operating systems and applications (NIST CSF ID.AM-3, CIS Control 7).
• Disable Password Authentication: Disable password-based SSH authentication and rely solely on SSH keys.

Business Impact & Risk Outlook

A successful SSH key compromise could lead to significant operational disruption, data breaches, and reputational damage. Attackers could gain unauthorized access to critical systems, exfiltrate sensitive data, or deploy ransomware. Legal and regulatory consequences may arise from data breaches. Expect an increase in automated SSH brute-forcing and key injection attempts over the next 3-6 months, driven by readily available exploit tools and cloud-based botnets.

Appendix

[Redacted Payload Snippet]

• Assumptions & Data Gaps: Sensor name and network port are unavailable. The specific payload content was redacted.
• References:
  • VirusTotal Sample

SGI is committed to helping organizations proactively manage and mitigate cybersecurity risks. To learn more about how we can help, consider a Request an Incident Readiness Review, explore our 24/7 Monitoring with Sentry365™, or engage our vCISO Advisory services.