By Charles Joseph | Cybersecurity Researcher

 Published on December 21st, 2024

Expansion buses, both legacy and modern, serve as critical pathways for connecting devices like storage, GPUs, and peripherals to a computer’s motherboard.

While modern buses like PCIe and Thunderbolt offer high speeds and efficiency, they also introduce cybersecurity challenges, such as Direct Memory Access (DMA) attacks and vulnerabilities from unauthorized physical or wireless connections.

Understanding the types, speeds, and security implications of expansion buses is essential for mitigating risks in both consumer and enterprise environments.

Expansion Buses and Their Cybersecurity Implications

1.) ISA (Industry Standard Architecture)

Type: Legacy
Speed: ~8 Mbps
Introduced: 1981, used until 1995
Description: ISA was one of the earliest internal expansion buses used in PCs, allowing for the addition of peripherals like sound cards and modems.
Cybersecurity Implications: ISA lacked encryption, authentication, or isolation mechanisms, making it vulnerable to physical tampering and eavesdropping. For example, an attacker could attach a rogue device to the ISA slot to monitor or manipulate data without being detected, as the system could not distinguish between authorized and unauthorized hardware.
Modern Solution: Modern systems use PCIe with support for isolation mechanisms like the Input-Output Memory Management Unit (IOMMU), which prevents unauthorized access to memory by rogue devices. Additionally, hardware authentication ensures only trusted devices can connect to the bus.

2.) EISA (Extended Industry Standard Architecture)

Type: Legacy
Speed: ~33 Mbps
Introduced: 1988, used until 2000
Description: EISA was a 32-bit version of ISA designed for server environments, offering more performance and device support.
Cybersecurity Implications: EISA, like ISA, lacked encryption or hardware-based isolation. An attacker with access to an EISA-equipped server could install a malicious network card to intercept traffic from other devices. For example, in a shared server room, an unauthorized user could exploit this by redirecting sensitive network packets to an external device for further analysis.
Modern Solution: Modern systems incorporate secure boot and device authentication to ensure only approved hardware is initialized and allowed to function. Additionally, virtualization technologies segment traffic to prevent unauthorized devices from intercepting data.

3.) PCI (Peripheral Component Interconnect)

Type: Legacy
Speed: Up to 533 MB/s
Introduced: 1992, used until 2010
Description: PCI became the dominant bus for internal peripherals like GPUs, NICs, and sound cards, replacing EISA and ISA.
Cybersecurity Implications: PCI was vulnerable to “bus sniffing,” where malicious hardware could intercept data flowing through the bus. For instance, if an attacker added a rogue PCI card to a system, it could silently monitor sensitive data, such as keystrokes from a keyboard or unencrypted network packets, due to the lack of data encryption or hardware security features.
Modern Solution: PCIe addresses this vulnerability with features like encryption on data paths, hardware integrity checks, and firmware validation to prevent unauthorized devices from accessing or intercepting bus traffic. IOMMU ensures that devices are only able to access memory they are explicitly allowed to.

4.) AGP (Accelerated Graphics Port)

Type: Legacy
Speed: Up to 2.1 GB/s
Introduced: 1997, used until 2008
Description: AGP was a high-speed connection dedicated to GPUs, offering better performance than PCI for graphics processing.
Cybersecurity Implications: AGP did not support encryption or authentication, but its limited function for graphics meant it was less likely to be exploited. However, an attacker could replace a legitimate graphics card with a malicious one containing a hidden data extraction chip. For example, such a device could steal rendered frame data or interfere with secure environments relying on GPU computations.
Modern Solution: GPUs in PCIe environments are subject to hardware attestation and secure initialization protocols, ensuring that only trusted hardware can function. Secure firmware updates prevent malicious alterations to the GPU’s behavior.

5.) SCSI (Small Computer System Interface)

Type: Legacy
Speed: Up to 320 MB/s
Introduced: 1986, used until 2010
Description: SCSI was used for connecting high-speed storage devices like hard drives and tape drives, popular in enterprise systems.
Cybersecurity Implications: SCSI devices lacked built-in encryption, making them vulnerable to physical attacks. For example, if an attacker physically accessed a SCSI-connected server, they could remove the SCSI drive and extract data using another system. Additionally, shared SCSI buses could expose data to unauthorized devices connected to the same bus.
Modern Solution: Modern storage systems use encryption at rest and transport encryption (e.g., AES encryption for enterprise drives) to ensure data cannot be accessed without authorization, even if drives are physically removed. Additionally, technologies like secure RAID configurations and hardware authentication prevent unauthorized devices from joining the system.

6.) Parallel Port

Type: Legacy (External)
Speed: ~2 Mbps
Introduced: 1970s, used until 2000s
Description: Parallel ports connected printers and external drives, offering a simple way to transfer data externally.
Cybersecurity Implications: Parallel ports had no encryption or access controls, meaning sensitive data like print jobs could be intercepted. For example, in a corporate environment, a malicious printer could log all documents sent through the parallel port, creating a major leak for sensitive data. Encryption wasn’t available at the port level, so secure printing would require software-based encryption before sending the data to the printer.
Modern Solution: Modern systems use USB or network printers with encrypted communication protocols such as IPP (Internet Printing Protocol) over HTTPS, ensuring print jobs remain secure during transmission.

7.) Serial Port

Type: Legacy (External)
Speed: Up to 115.2 Kbps
Introduced: 1960s, used until 2000s
Description: Serial ports were used for connecting modems, mice, and other peripherals, commonly used in older systems.
Cybersecurity Implications: Serial ports were vulnerable to remote access attacks if connected to insecure devices, such as modems. Attackers could exploit weak authentication protocols to gain unauthorized access to systems. For example, if a dial-up modem was connected to a serial port, an attacker could brute force the system’s credentials and establish unauthorized access to the network.
Modern Solution: Serial ports have been replaced by USB or Ethernet-based devices that support encryption and modern authentication protocols like WPA3 or TLS to secure remote connections.

8.) FireWire (IEEE 1394)

Type: Legacy (External)
Speed: Up to 800 Mbps
Introduced: 1995, used until 2013
Description: FireWire was a high-speed external bus used for video cameras, external hard drives, and other peripherals requiring fast data transfer.
Cybersecurity Implications: FireWire posed a significant risk due to its Direct Memory Access (DMA) feature, which allowed connected devices to bypass the operating system and access system memory directly. An attacker with physical access could use a malicious FireWire device to exploit this feature and compromise the system. For example, an attacker could use a specially crafted FireWire device to extract encryption keys or sensitive data from the system’s memory.
Modern Solution: Thunderbolt, the successor to FireWire, implements IOMMU and Thunderbolt Security Levels to restrict DMA access to authorized devices. These features prevent unauthorized memory access from malicious devices.

9.) PCIe (Peripheral Component Interconnect Express)

Type: Modern
Speed: PCIe 3.0: 32 GB/s (x16), PCIe 4.0: 64 GB/s (x16), PCIe 5.0: 128 GB/s (x16)
Introduced: 2003, still in use
Description: PCIe is the dominant expansion bus in modern systems, used for GPUs, SSDs, network cards, and more. It offers extremely high speeds and scalability.
Cybersecurity Implications: PCIe, while advanced, is vulnerable to Direct Memory Access (DMA) attacks if the system does not have Input-Output Memory Management Unit (IOMMU) protection enabled. A malicious device connected to a PCIe slot could access system memory directly, allowing for data theft, memory injection attacks, or bypassing OS security controls. For example, an attacker with physical access could install a rogue PCIe device that silently exfiltrates encryption keys or sensitive data.
Modern Solution: Modern systems implement IOMMU to restrict DMA access to authorized devices only. Additionally, secure boot and firmware validation ensure that malicious devices cannot operate or exploit vulnerabilities in the system. Endpoint security software can also monitor for unauthorized hardware.

10.) M.2

Type: Modern
Speed: Up to 7 GB/s (PCIe Gen4), 600 MB/s (SATA III)
Introduced: 2013, still in use
Description: M.2 is a compact form factor for SSDs and other peripherals. It connects via PCIe or SATA and is widely used in modern laptops and desktops.
Cybersecurity Implications: M.2 drives are vulnerable to physical theft, as the data stored on them is often unencrypted. An attacker could remove an M.2 drive from a laptop or desktop and access its contents on another system. This is particularly dangerous in corporate environments where sensitive data like customer records or intellectual property might be stored. For instance, a stolen M.2 drive from an unencrypted laptop could result in a major data breach.
Modern Solution: Full-disk encryption, such as BitLocker or LUKS, ensures that even if the M.2 drive is stolen, the data cannot be accessed without the decryption key. Many enterprise environments also use physical security features, such as laptop locks, to deter theft.

11.) SATA (Serial ATA)

Type: Modern
Speed: ~600 MB/s (SATA III)
Introduced: 2000, still in use
Description: SATA is used for connecting hard drives, SSDs, and optical drives. It is slower than PCIe but remains widely used for storage.
Cybersecurity Implications: SATA-connected storage devices are vulnerable to unauthorized access if encryption is not enabled. Attackers can physically remove the drive and access its data on another system. For example, an attacker could extract an unencrypted SATA hard drive from a corporate workstation and use data recovery tools to retrieve sensitive files. Shared systems that allow multiple users to access SATA-connected storage are also at risk of accidental or intentional data leaks.
Modern Solution: Modern drives often support hardware encryption (such as TCG Opal standards), which encrypts data at the device level. Operating systems also support software-based encryption tools to secure data. Physical security measures, such as locking drive bays, add an additional layer of protection.

12.) U.2

Type: Modern
Speed: Up to 32 GB/s (PCIe Gen3)
Introduced: 2012, still in use
Description: U.2 is an enterprise-grade form factor for SSDs, offering high-speed storage solutions for servers and workstations.
Cybersecurity Implications: U.2 drives, often used in data centers and enterprise systems, are vulnerable to unauthorized access if drives are stolen or improperly decommissioned. For example, a decommissioned U.2 SSD that still contains sensitive customer data could be recovered and exploited by an attacker. Shared systems also present risks of unauthorized access to data stored on the drives.
Modern Solution: Enterprise systems implement drive encryption standards such as AES-256 to secure data at rest. Secure disposal practices, such as physical destruction of drives or cryptographic erasure, ensure that sensitive data cannot be recovered. Many data centers also use tamper-evident seals and secure storage racks to prevent unauthorized drive access.

13.) USB (Universal Serial Bus)

Type: Modern (External)
Speed: USB 3.2: Up to 20 Gbps, USB4: Up to 40 Gbps
Introduced: 1996, still in use
Description: USB is the most common external bus for peripherals, ranging from keyboards and mice to external drives and printers.
Cybersecurity Implications: USB devices are highly versatile but present numerous security risks. Malicious devices can exploit vulnerabilities like BadUSB to inject malware into a host system. Additionally, unencrypted USB drives can be stolen or lost, resulting in significant data breaches. For instance, an attacker could distribute infected USB drives in a public setting (e.g., a parking lot), which unsuspecting users might plug into their systems, compromising them.
Modern Solution: USB security is addressed by restricting access to authorized devices using endpoint protection tools. Encryption software can secure data stored on USB drives, and modern USB standards support device authentication to prevent unauthorized access. Organizations often implement strict USB policies, including disabling USB ports entirely for security-critical systems.

14.) Thunderbolt

Type: Modern (External)
Speed: Up to 40 Gbps
Introduced: 2011, still in use
Description: Thunderbolt is a high-speed external bus used for displays, external SSDs, and docking stations. It supports daisy-chaining multiple devices.
Cybersecurity Implications: Like FireWire, Thunderbolt’s Direct Memory Access (DMA) feature makes it vulnerable to attacks. If IOMMU is disabled, an attacker can connect a malicious Thunderbolt device to access the system’s memory directly, potentially stealing encryption keys or sensitive data. For example, a rogue docking station could exfiltrate sensitive information from laptops connected to it.
Modern Solution: Thunderbolt Security Levels and IOMMU ensure that only authorized devices can access system memory. Operating systems like macOS and Windows now require explicit user approval before initializing Thunderbolt devices. Firmware updates and tamper-proof cables further mitigate risks.

15.) eSATA (External SATA)

Type: Modern (External)
Speed: Up to 6 Gbps (~600 MB/s)
Introduced: 2004, used until 2015
Description: eSATA was an external version of SATA designed for connecting external drives directly to a system.
Cybersecurity Implications: eSATA had no built-in encryption, making it susceptible to unauthorized data access. For instance, an attacker could steal an eSATA-connected drive from a workstation and read its contents on another device. The lack of device authentication also meant that unauthorized drives could be plugged in to overwrite or steal data.
Modern Solution: Modern external storage solutions have largely transitioned to USB or Thunderbolt, which include features like encryption and device authentication. Additionally, organizations now enforce encryption standards on all external drives to prevent unauthorized access.

16.) Bluetooth

Type: Modern (Wireless)
Speed: ~3 Mbps (Bluetooth 5.0)
Introduced: 1999, still in use
Description: Bluetooth enables wireless connectivity for peripherals like headphones, keyboards, and mice.
Cybersecurity Implications: Bluetooth is susceptible to pairing vulnerabilities, man-in-the-middle (MITM) attacks, and malware injection. For example, attackers can exploit insecure Bluetooth connections to intercept data or inject malicious commands into a system. A notable example is the BlueBorne attack, which allowed attackers to exploit Bluetooth vulnerabilities to take control of devices without requiring user interaction.
Modern Solution: Modern Bluetooth standards, such as Bluetooth 5.0, include stronger encryption and pairing protocols to protect against attacks. Operating systems also enforce strict Bluetooth permissions, requiring user approval before pairing new devices. Organizations may disable Bluetooth in high-security environments to eliminate risks altogether.

17.) Wi-Fi

Type: Modern (Wireless)
Speed: Wi-Fi 6: Up to 9.6 Gbps
Introduced: 1997, still in use
Description: Wi-Fi enables wireless connectivity for computers, smartphones, and IoT devices, providing high-speed network access.
Cybersecurity Implications: Wi-Fi networks are vulnerable to data interception, rogue access points, and brute-force attacks on weak passwords. For example, attackers could use packet sniffing tools to intercept unencrypted network traffic or exploit poorly secured public Wi-Fi hotspots to compromise user devices.
Modern Solution: Modern Wi-Fi standards, such as WPA3, encrypt all traffic between devices and access points to prevent interception. Network administrators can implement measures like MAC address filtering, disabling SSID broadcasting, and segmenting guest networks to further enhance security.

Summary

Expansion buses are vital components of computer architecture, enabling devices like GPUs, SSDs, and peripherals to connect and communicate with the system.

Over the years, these buses have evolved from legacy technologies like ISA and PCI to modern high-speed interfaces such as PCIe, M.2, and Thunderbolt.

While these advancements offer significant improvements in speed and efficiency, they also bring new cybersecurity challenges, such as vulnerabilities to unauthorized access, data interception, and hardware tampering.

To safeguard against these risks, it is important to implement encryption, hardware isolation, and secure access controls for both legacy and modern expansion bus technologies.