TFTP Boot
TFTP Boot [T1542.005]
Last updated
TFTP Boot [T1542.005]
Last updated
Name: TFTP Boot
ID: T1542.005
Tactics: ,
Technique:
TFTP Boot (Technique ID T1542.005) is a sub-technique within the MITRE ATT&CK framework under the "Pre-OS Boot" persistence category. Attackers leverage the Trivial File Transfer Protocol (TFTP) boot functionality to maintain persistence by manipulating boot mechanisms. This technique involves configuring compromised systems to load malicious software or configurations during the pre-boot environment, often bypassing standard operating system security mechanisms.
The TFTP Boot technique exploits the network-based boot mechanism typically used by devices to load operating systems or configurations from a remote server. TFTP (Trivial File Transfer Protocol) is a lightweight protocol commonly implemented in network boot scenarios due to its simplicity and minimal overhead. Attackers may abuse TFTP boot environments by:
Modifying boot configuration files (such as PXE boot configurations) to redirect the boot process to malicious payloads.
Hosting malicious boot images or kernel modules on attacker-controlled TFTP servers, causing compromised systems to execute malicious code during the boot stage.
Leveraging DHCP server manipulation to direct victim machines to attacker-controlled TFTP servers, allowing injection of malicious boot images.
Technical mechanisms and execution methods include:
PXE Boot Manipulation:
Attackers compromise or spoof DHCP servers to point clients to malicious TFTP servers.
Victims' systems download and execute attacker-controlled boot images.
Malicious Boot Images:
Attackers craft specialized boot images containing backdoors, rootkits, or malicious kernel modules.
These boot images are hosted on attacker-controlled TFTP servers and loaded onto victim systems during the boot process.
Network Infrastructure Compromise:
Attackers compromise legitimate network infrastructure (DHCP/TFTP servers) to distribute malicious boot configurations and images.
This allows attackers to maintain persistence and control over victim systems at the earliest stages of the boot process.
Attackers typically utilize TFTP Boot in scenarios involving:
Persistence and Long-term Access:
Maintaining covert, persistent access to compromised systems by embedding malicious code into the boot process.
Ensuring persistence even after the operating system is reinstalled or replaced.
Initial Access and Lateral Movement:
Exploiting network boot environments to compromise multiple systems across a network simultaneously.
Leveraging compromised DHCP/TFTP infrastructure for lateral movement within internal networks.
Supply Chain Attacks:
Injecting malicious boot images into legitimate network boot environments during software or hardware deployment phases.
Targeting organizations relying heavily on network boot functionality for system provisioning and maintenance.
Advanced Persistent Threat (APT) Campaigns:
Highly targeted attacks by sophisticated threat actors seeking stealthy, persistent footholds in secure environments.
Exploiting trusted boot processes to evade traditional endpoint detection and response (EDR) solutions.
Detection of TFTP Boot compromise typically involves monitoring and analyzing network infrastructure, network traffic, and boot configurations. Common detection methods include:
Network Traffic Analysis:
Monitoring network traffic for unusual DHCP responses or unauthorized TFTP connections.
Identifying connections to unknown or unauthorized TFTP servers.
DHCP Server Monitoring:
Regular auditing of DHCP configurations to detect unauthorized changes or suspicious boot file pointers.
Alerting on anomalies in DHCP lease assignments or boot server IP addresses.
Boot Configuration Integrity Checks:
Regularly verifying the integrity and authenticity of PXE boot configuration files.
Implementing file integrity monitoring solutions to detect unauthorized modifications of boot images or related configuration files.
Endpoint and Server Logs Analysis:
Reviewing logs on DHCP and TFTP servers for unusual access patterns, failed authentication attempts, or unauthorized file transfers.
Correlating log data to detect anomalous boot requests or image downloads.
Indicators of Compromise (IoCs) specific to TFTP Boot attacks may include:
Unfamiliar boot image filenames or hashes appearing within TFTP server logs.
DHCP server configuration changes pointing to suspicious or unknown TFTP servers/IP addresses.
Unexpected or unauthorized systems performing PXE boot operations.
Unusual network traffic patterns indicating boot image transfers from unknown or external hosts.
Detecting TFTP Boot attacks promptly is critical due to their severe impacts and stealthy nature. Importance includes:
Early-stage Persistence Prevention:
Prevent attackers from establishing deep-rooted and persistent footholds within the network infrastructure.
Reduce the risk of long-term compromise that survives operating system reinstallations or endpoint security measures.
Minimizing Attack Surface:
Early detection helps limit attackers' ability to spread laterally or escalate privileges across the network.
Prevents attackers from embedding malicious code at critical boot stages, significantly reducing remediation complexity.
Protecting Critical Infrastructure:
Network boot environments are often used in critical or sensitive environments, such as data centers, industrial control systems, or enterprise deployments.
Early detection prevents attackers from compromising critical systems or disrupting essential operations.
Reducing Operational Impact:
Timely detection limits potential downtime, data loss, or financial damage from compromised boot environments.
Mitigates the risk of attackers leveraging boot-level persistence to evade traditional security controls and detection mechanisms.
Real-world examples of TFTP Boot attacks and scenarios include:
FIN7 Group Attacks:
FIN7 threat actors have reportedly leveraged compromised network infrastructure, including DHCP and TFTP servers, to distribute malicious boot images and payloads.
Attackers targeted retail and hospitality sectors, deploying malicious boot images to achieve persistence and lateral movement within victim networks.
APT41 Boot Image Manipulation:
APT41 has been observed manipulating PXE boot environments to deploy malicious kernel modules and rootkits.
Attackers compromised internal network infrastructure, redirecting boot requests to attacker-controlled TFTP servers to maintain persistent access to targeted organizations.
Supply Chain Attack via Network Boot:
Attackers compromised an organization's internal TFTP server used for provisioning new systems.
Malicious boot images containing rootkits were distributed to newly provisioned endpoints, allowing attackers to gain persistent access to multiple systems within the organization.
Internal Red Team Engagements:
Security teams and penetration testers frequently demonstrate the feasibility of TFTP Boot attacks during internal security assessments.
Commonly used tools and frameworks in these engagements include PXEThief, custom-crafted boot images, and DHCP/TFTP spoofing tools.
Tools commonly associated with TFTP Boot attacks include:
PXEThief: Tool designed to automate DHCP and TFTP spoofing attacks.
Dnsmasq: Legitimate DHCP/TFTP server software frequently used by attackers for malicious boot image hosting.
Custom Linux Kernel Images: Attackers often craft customized Linux kernels or boot images embedding rootkits, backdoors, or malicious modules for persistent access.
Impacts observed from these real-world examples include:
Persistent, stealthy attacker presence within critical network infrastructure.
Significant challenges in detection and remediation due to boot-level persistence.
Potential for widespread compromise through lateral movement facilitated by compromised boot environments.
Elevated risks of data exfiltration, espionage, and operational disruption due to attacker control at the earliest stages of system initialization.