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Posted on Jul 29

SFTP threat model by Claude

SFTP Machine-to-Machine Threat Model

STRIDE Methodology + MITRE ATT&CK Framework

System Architecture Overview

Components:

Client Server (Server A): Initiates SFTP connections, automated file transfers
SFTP Server (Server B): Receives connections, hosts files, manages access
Network Infrastructure: Routers, switches, firewalls between servers
Credential Management: Key stores, certificate authorities, secret management
File Systems: Local and shared storage for file operations
Monitoring Systems: Logs, SIEM, security monitoring tools

Trust Boundaries:

Network perimeter (internal vs external networks)
Server boundaries (OS kernel, application space)
Credential storage boundaries
File system access boundaries

S - SPOOFING IDENTITY

Threat Scenarios & MITRE ATT&CK Techniques

T1.1: Server Identity Spoofing

MITRE Techniques:

T1557.002 - Man-in-the-Middle: ARP Cache Poisoning
- Attacker poisons ARP tables to intercept traffic
- Redirects SFTP connections to malicious server
T1590.005 - Gather Victim Network Information: IP Addresses
- Reconnaissance to identify target server addresses
T1556.003 - Modify Authentication Process: Pluggable Authentication Modules
- Compromise authentication mechanisms on target server

Attack Vectors:

DNS spoofing/cache poisoning to redirect Server A to malicious endpoint
BGP hijacking to route traffic through attacker infrastructure
Certificate authority compromise to issue fraudulent certificates

T1.2: Client Credential Compromise

MITRE Techniques:

T1552.004 - Unsecured Credentials: Private Keys
- Extract SSH private keys from compromised systems
T1555.003 - Credentials from Password Stores: Credentials from Web Browsers
- Harvest stored credentials from management interfaces
T1078.002 - Valid Accounts: Domain Accounts
- Use compromised service accounts for unauthorized access

Attack Vectors:

Memory dumping to extract private keys from running processes
File system access to steal credential files
Supply chain attacks targeting credential management tools

Countermeasures:

C1.1: Certificate pinning and HPKP (HTTP Public Key Pinning)
C1.2: Mutual TLS authentication with hardware-backed certificates
C1.3: Network monitoring for ARP/DNS anomalies
C1.4: Regular credential rotation with automated key management

T - TAMPERING WITH DATA

Threat Scenarios & MITRE ATT&CK Techniques

T2.1: Data Modification in Transit

MITRE Techniques:

T1040 - Network Sniffing
- Capture network traffic for analysis and modification
T1557.001 - Man-in-the-Middle: LLMNR/NBT-NS Poisoning
- Intercept and modify network communications
T1601.002 - Modify System Image: Downgrade System Image
- Force use of weaker encryption protocols

Attack Vectors:

SSL/TLS downgrade attacks forcing weaker ciphers
Protocol manipulation to bypass integrity checks
Network appliance compromise for traffic modification

T2.2: File System Tampering

MITRE Techniques:

T1565.001 - Data Manipulation: Stored Data Manipulation
- Modify files on source or destination servers
T1070.004 - Indicator Removal on Host: File Deletion
- Remove evidence of file tampering
T1222.002 - File and Directory Permissions Modification: Linux and Mac File and Directory Permissions Modification
- Alter permissions to enable unauthorized access

Attack Vectors:

Rootkit installation for persistent file system access
Backup system compromise to modify archived files
Configuration file tampering to alter transfer behavior

Countermeasures:

C2.1: End-to-end encryption with authenticated encryption modes
C2.2: File integrity monitoring (FIM) with cryptographic hashes
C2.3: Immutable infrastructure and infrastructure as code
C2.4: Digital signatures for critical files and configurations

R - REPUDIATION

Threat Scenarios & MITRE ATT&CK Techniques

T3.1: Log Tampering and Evidence Destruction

MITRE Techniques:

T1070.001 - Indicator Removal on Host: Clear Windows Event Logs
- Delete authentication and transfer logs
T1070.002 - Indicator Removal on Host: Clear Linux or Mac System Logs
- Remove evidence of unauthorized activities
T1562.002 - Impair Defenses: Disable Windows Event Logging
- Prevent future logging of activities

Attack Vectors:

Log server compromise to modify audit trails
Time synchronization attacks to create timeline confusion
Credential theft to perform actions under legitimate identities

T3.2: Transaction Denial

MITRE Techniques:

T1070.006 - Indicator Removal on Host: Timestomp
- Modify file timestamps to hide activities
T1036.005 - Masquerading: Match Legitimate Name or Location
- Disguise malicious activities as legitimate operations

Countermeasures:

C3.1: Immutable audit logging with cryptographic integrity
C3.2: Multi-destination log streaming to prevent single point of failure
C3.3: Blockchain-based audit trails for critical transactions
C3.4: Time synchronization with authenticated NTP servers

I - INFORMATION DISCLOSURE

Threat Scenarios & MITRE ATT&CK Techniques

T4.1: Credential and Key Exposure

MITRE Techniques:

T1552.001 - Unsecured Credentials: Credentials In Files
- Extract credentials from configuration files
T1005 - Data from Local System
- Access sensitive files on compromised systems
T1140 - Deobfuscate/Decode Files or Information
- Decrypt or decode stored credential material

Attack Vectors:

Memory forensics to extract encryption keys
Configuration file exposure through web servers
Environment variable disclosure in process listings

T4.2: Traffic Analysis and Data Interception

MITRE Techniques:

T1040 - Network Sniffing
- Capture and analyze network traffic patterns
T1020 - Automated Exfiltration
- Systematically steal data through compromised channels
T1041 - Exfiltration Over C2 Channel
- Use command and control infrastructure for data theft

Attack Vectors:

Side-channel attacks on encryption implementations
Traffic pattern analysis to infer sensitive information
Compromised network infrastructure for data collection

Countermeasures:

C4.1: Hardware Security Modules (HSMs) for key protection
C4.2: Perfect Forward Secrecy (PFS) in all encrypted communications
C4.3: Traffic padding and dummy transactions to obscure patterns
C4.4: Zero-knowledge architecture for credential management

D - DENIAL OF SERVICE

Threat Scenarios & MITRE ATT&CK Techniques

T5.1: Resource Exhaustion Attacks

MITRE Techniques:

T1498.001 - Network Denial of Service: Direct Network Flood
- Overwhelm network infrastructure with traffic
T1499.004 - Endpoint Denial of Service: Application or System Exploitation
- Exploit application vulnerabilities to cause crashes
T1565.003 - Data Manipulation: Runtime Data Manipulation
- Modify system behavior to cause resource exhaustion

Attack Vectors:

SSH connection flooding to exhaust server resources
Large file upload attacks to consume storage
Fork bomb attacks through compromised accounts

T5.2: Infrastructure Disruption

MITRE Techniques:

T1489 - Service Stop
- Stop critical services required for SFTP operations
T1529 - System Shutdown/Reboot
- Force system restarts to disrupt operations
T1485 - Data Destruction
- Delete critical system files or configurations

Countermeasures:

C5.1: Rate limiting and connection throttling
C5.2: Resource quotas and monitoring with automated responses
C5.3: Redundant infrastructure with automated failover
C5.4: DDoS protection at multiple network layers

E - ELEVATION OF PRIVILEGE

Threat Scenarios & MITRE ATT&CK Techniques

T6.1: SSH Service Exploitation

MITRE Techniques:

T1068 - Exploitation for Privilege Escalation
- Exploit SSH daemon vulnerabilities for root access
T1055.012 - Process Injection: Process Hollowing
- Inject malicious code into SSH processes
T1543.002 - Create or Modify System Process: Systemd Service
- Create persistent backdoors through system services

Attack Vectors:

Buffer overflow attacks against SSH implementations
Configuration vulnerabilities (weak ciphers, root login enabled)
Race condition exploits in file handling

T6.2: Container and Virtualization Escapes

MITRE Techniques:

T1611 - Escape to Host
- Break out of containerized environments
T1055.001 - Process Injection: Dynamic-link Library Injection
- Inject malicious libraries into running processes
T1134.001 - Access Token Manipulation: Token Impersonation/Theft
- Steal and impersonate privileged access tokens

Attack Vectors:

Container runtime vulnerabilities for host access
Kernel exploits through syscall interfaces
Shared resource exploitation (shared volumes, networks)

T6.3: Lateral Movement

MITRE Techniques:

T1021.004 - Remote Services: SSH
- Use compromised credentials for lateral movement
T1550.003 - Use Alternate Authentication Material: Pass the Ticket
- Reuse authentication tokens across systems
T1080 - Taint Shared Content
- Modify shared files to compromise additional systems

Countermeasures:

C6.1: Principle of least privilege with mandatory access controls
C6.2: Container security with runtime protection
C6.3: Regular vulnerability scanning and automated patching
C6.4: Network microsegmentation and zero-trust architecture

Advanced Persistent Threat (APT) Scenarios

APT Scenario 1: Supply Chain Compromise

MITRE Techniques Chain:

T1195.002 - Supply Chain Compromise: Compromise Software Supply Chain
T1554 - Compromise Client Software Binary
T1078.002 - Valid Accounts: Domain Accounts
T1020 - Automated Exfiltration

Attack Flow:

Compromise SFTP client software or libraries
Establish persistent backdoor in client systems
Harvest credentials and perform automated data exfiltration
Use legitimate channels to avoid detection

APT Scenario 2: Living Off The Land

MITRE Techniques Chain:

T1078.003 - Valid Accounts: Local Accounts
T1021.004 - Remote Services: SSH
T1083 - File and Directory Discovery
T1005 - Data from Local System
T1041 - Exfiltration Over C2 Channel

Attack Flow:

Compromise legitimate service accounts
Use SSH for authorized but malicious access
Perform reconnaissance using standard system tools
Exfiltrate data through legitimate protocols

Risk Assessment Matrix

Threat ID	STRIDE Category	MITRE Technique	Likelihood	Impact	Risk Level
T1.1	Spoofing	T1557.002	Medium	High	High
T1.2	Spoofing	T1552.004	High	Critical	Critical
T2.1	Tampering	T1040, T1557.001	Low	High	Medium
T2.2	Tampering	T1565.001	Medium	High	High
T3.1	Repudiation	T1070.001/002	Medium	Medium	Medium
T4.1	Info Disclosure	T1552.001	High	Critical	Critical
T4.2	Info Disclosure	T1040	Medium	High	High
T5.1	DoS	T1498.001	High	Medium	Medium
T5.2	DoS	T1489	Low	High	Medium
T6.1	Privilege Escalation	T1068	Low	Critical	High
T6.2	Privilege Escalation	T1611	Medium	Critical	High
T6.3	Privilege Escalation	T1021.004	High	High	Critical

Detection and Monitoring Framework

MITRE ATT&CK-Based Detection Rules

Credential Access Detection:

- Monitor for: T1552.004 (Private Keys)
  - File access to .ssh directories
  - Unusual process access to key files
  - Memory dumps of SSH processes

- Monitor for: T1555.003 (Password Stores)
  - Access to credential management APIs
  - Unusual queries to secret management systems

Lateral Movement Detection:

- Monitor for: T1021.004 (SSH)
  - SSH connections from unusual source IPs
  - Multiple failed authentication attempts
  - SSH sessions outside normal business hours
  - Connections to unusual destination ports

Defense Evasion Detection:

- Monitor for: T1070.001/002 (Log Clearing)
  - Log deletion events
  - Log service stopping/starting
  - Unusual log volume changes

Behavioral Analytics

Baseline normal M2M communication patterns
Detect anomalies in file transfer volumes, timing, and destinations
Monitor for unusual network traffic patterns
Track credential usage patterns and detect anomalies

Implementation Roadmap

Phase 1: Critical Risk Mitigation (0-30 days)

Implement secure credential management (HSM/Vault)
Deploy certificate-based authentication
Enable comprehensive audit logging
Implement network monitoring for ATT&CK techniques

Phase 2: Defense in Depth (30-90 days)

Deploy file integrity monitoring
Implement network microsegmentation
Set up behavioral analytics and anomaly detection
Establish incident response procedures

Phase 3: Advanced Security (90+ days)

Deploy zero-trust architecture
Implement advanced threat hunting capabilities
Establish threat intelligence integration
Conduct regular red team exercises

Continuous Operations

Monthly credential rotation
Quarterly vulnerability assessments
Annual penetration testing with MITRE ATT&CK framework
Continuous monitoring and alerting
Regular threat model updates based on new attack techniques