Executive Summary

• SGI detected a potentially malicious file delivered via web traffic containing SSH authorized keys.
• The affected system is likely a Linux-based server or workstation.
• The likely objective is unauthorized remote access via SSH.
• The business risk is low due to the low severity rating, but could escalate to high if successful.

We anticipate an increase in automated attacks targeting SSH keys to gain unauthorized access to systems.

Observed Activity (SGI Sensors)

SGI sensors detected a suspicious connection from IP address 209.141.41.212. The connection involved the transfer of a file, which was identified as containing SSH authorized keys. This event suggests a potential attempt to inject malicious SSH keys onto the targeted system, potentially leading to unauthorized remote access. The source ASN is FranTech Solutions, based in the US.

Malware/Technique Overview

The detected file contains SSH authorized keys, suggesting an attempt to inject malicious keys into the ~/.ssh/authorized_keys file of user accounts. This would allow the attacker to gain unauthorized SSH access to the system without needing to know the user’s password. The file was delivered via web, so we can assume that the initial access was likely via exploitation of a web vulnerability or a phishing attack that tricked a user into downloading the file. This attack vector is often used to deploy botnet agents or crypto miners.

• T1190 – Exploit Public-Facing Application
• T1189 – Drive-by Compromise
• T1133 – External Remote Services
• T1059.004 – Command and Scripting Interpreter: Unix Shell
• T1078.004 – Valid Accounts: Cloud Accounts (if applicable)

VirusTotal Snapshot

VirusTotal analysis indicates that 29 out of 62 vendors flagged the file as malicious, while 33 vendors did not detect it. The file is identified as HTML and has a size of 389 bytes. Based on the aliases, this file and similar files have been seen targeting various user accounts. This suggests a broad, automated campaign. The file has a VirusTotal reputation score of -34.

Notable aliases include:

• 20251003-023501-8bc8da5545ea-1-redir__root__ssh_authorized_keys
• 20251001-193039-f28007d18ed1-1-redir__home_seekcy__ssh_authorized_keys
• authorized_keys

• VirusTotal Sample

Indicators of Compromise (IoCs)

Monitor these IoCs for at least 30 days.

Detection & Hunting

Splunk SPL

index=* source=web_logs src_ip=209.141.41.212 
| regex _raw="ssh-rsa AAAA[0-9A-Za-z+/]+"
| table _time, src_ip, dest_ip, _raw

Elastic/Kibana KQL

source.ip : "209.141.41.212" AND message : "ssh-rsa AAAA"

These queries identify connections from the malicious IP address that contain SSH public key patterns. Validate any positive results to confirm unauthorized SSH activity and eliminate false positives.

Containment, Eradication & Recovery

1. Isolate: Disconnect the affected system from the network to prevent further compromise.
2. Block: Block the malicious IP address (209.141.41.212) at the firewall.
3. Scan: Perform a full system scan with updated antivirus and anti-malware software.
4. Reimage (if needed): If the system is heavily compromised, reimage it from a known good backup.
5. Credential Resets: Reset passwords for all user accounts on the affected system and any related accounts.

Inform the IT and leadership teams about the incident, progress on containment, and any remediation steps. Also ensure to preserve evidence for potential forensic analysis.

Hardening & Preventive Controls

• Multi-Factor Authentication (MFA): Implement MFA for all remote access services, including SSH (NIST CSF: PR.AC-1, CIS Control 6).
• Endpoint Detection and Response (EDR): Tune EDR solutions to detect suspicious file downloads and SSH key modifications (NIST CSF: DE.CM-1, CIS Control 10).
• Network Segmentation: Implement network segmentation to limit the blast radius of a potential compromise (NIST CSF: PR.AC-5, CIS Control 14).
• Least Privilege: Enforce the principle of least privilege to limit user access to only what is necessary (NIST CSF: PR.AC-3, CIS Control 5).
• Patch Management: Maintain strict patch SLAs to address vulnerabilities in a timely manner (NIST CSF: ID.AM-3, CIS Control 7).
• SSH Hardening: Disable password-based SSH authentication and only allow key-based authentication. Regularly rotate SSH keys.

Business Impact & Risk Outlook

A successful SSH key compromise can lead to significant operational disruption, data breaches, and reputational damage. Legal risks could arise if sensitive data is accessed and exfiltrated. This incident underscores the importance of robust security controls for remote access. Expect an increase in attacks targeting remote access services in the next 3-6 months.

Appendix

Assumptions & Data Gaps:

• The specific vulnerability exploited to deliver the payload is unknown.
• The targeted user accounts are unknown.
• The ultimate goal of the attacker post-compromise remains unclear.
• Sensor name and network port are not provided.

References:

• VirusTotal Sample

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