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Hackers Can Plant Backdoors on Bare Metal Cloud Servers: Researchers

Malicious actors could plant firmware backdoors on bare metal cloud servers and use them to disrupt applications, steal data, and launch ransomware attacks, firmware security company Eclypsium warned on Tuesday.

Malicious actors could plant firmware backdoors on bare metal cloud servers and use them to disrupt applications, steal data, and launch ransomware attacks, firmware security company Eclypsium warned on Tuesday.

Bare metal cloud services provide organizations the hardware needed to run their applications, without providing a hypervisor. Unlike in the case of other types of cloud services, where a server can have multiple tenants, bare metal services provide exclusive access to the entire physical server. Once a customer no longer needs the server, the hardware is reassigned to another customer.

Researchers at Eclypsium discovered that hackers could plant firmware backdoors on these servers that can later be leveraged against the device’s next customer. The attack method has been dubbed “Cloudborne.”

Eclypsium believes this problem affects many bare metal services providers, but it has conducted tests on IBM’s SoftLayer cloud services “because of its simplified logistics and access to hardware.”

Cloudborne attack targets bare metal cloud serversAn analysis of these servers revealed that some of them use hardware provided by SuperMicro. Eclypsium had previously identified vulnerabilities in SuperMicro products, specifically ones related to the Baseboard Management Controller (BMC).

The BMC is a small computer present on a majority of server motherboards. Its Intelligent Platform Management Interface (IPMI) component allows administrators to remotely control and monitor a server without having to access the operating system or applications running on it. The BMC can be used to reboot a device, install an operating system, update the firmware, monitor system parameters, and analyze logs.

Eclypsium has demonstrated that attackers can load malicious code onto the BMC in an effort to gain persistent access and control over the system, and even to remotely brick a server.

The researchers started their analysis of IBM SoftLayer services by acquiring a server and making small and benign changes to its BMC firmware. Eclypsium noted that the modifications it had made – one character was changed in a configuration file (bitflip) and a new IPMI user with admin privileges was added – did not involve the exploitation of any vulnerabilities and instead were changes that any customer could make.

The experts then released the server back to IBM and used a different account to acquire the same device. They noticed that while the IPMI user had been removed as part of the vendor’s reclamation process, the firmware containing the flipped bit was unchanged. They also noticed that BMC logs were still there and the BMC root password was the same.

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“The combination of using vulnerable hardware and not reflashing the firmware makes it possible for a malicious party to implant the server’s BMC code and inflict damage or steal data from IBM clients that use that server in the future,” Eclypsium researchers said.

“By not deleting the logs, a new customer could gain insight into the actions and behaviors of the previous owner of the device, while knowing the BMC root password could enable an attacker to more easily gain control over the machine in the future,” they added.

According to the security firm, an attacker could make BMC firmware changes that would cause a permanent denial-of-service (DoS) attack and brick the server. They could also plant a backdoor that would give them access to the data stored on the device by the next customer.

“Additionally attacks against the firmware on drives and network adapters themselves can provide attackers with another very low-level way of stealing or intercepting data. Likewise with low-level control over the server and network adapters, the attacker would have a variety of options for exfiltrating data out of the cloud environment,” Eclypsium explained.

The attack method can also be used to launch ransomware attacks, where the attacker threatens to disrupt applications and damage data.

Eclypsium notified IBM of its findings, but it initially appeared that the tech giant had ignored its messages. However, IBM has been working on addressing the issue in response to Eclypsium’s research, even if it has not provided any feedback to the security firm.

“We are not aware of any client or IBM data being put at risk because of this reported potential vulnerability and we have taken actions to eliminate the vulnerability. Given the remediation steps we have taken and the level of difficulty required to exploit this vulnerability, we believe the potential impact to clients is low,” an IBM spokesperson told SecurityWeek. “While the report focuses on IBM, this was actually a potential industry-wide vulnerability for all cloud service providers and we thank Eclypsium for bringing it to the attention of the industry.”

In an advisory published on Monday, IBM says it’s now forcing all BMCs to be reflashed with factory firmware before being passed on to other customers. The company says it will also delete all logs and regenerate all passwords for the BMC firmware.

However, Eclypsium claimed that the server targeted in their tests still contained the firmware modifications when checked on Monday. Moreover, the company does not agree with IBM’s assessment that this is a “low severity” issue, noting that its CVSS score is 9.3, which puts it in the “critical severity” category.

“While the hardware specifications of BMC hardware are low as compared with the host server, the capability for security-critical impact is high,” Eclypsium argued. “By design, the BMC is intended for managing the host system, and as such, it is more privileged than the host. The BMC has continual access to files, memory (using DMA), keyboard/video, and firmware of the host (which is required because it needs the ability to reinstall/reconfigure it). Furthermore, the BMC is able to send data to an external network, even potentially reconfiguring the host network interface. This provides an attacker with all the tools necessary for complete and stealthy control of a victim system.”

Related: 3 Public Cloud Security Myths Debunked

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Written By

Eduard Kovacs (@EduardKovacs) is a managing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.

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