Researchers at firmware security company Eclypsium discovered that the baseboard management controller (BMC) shipped with some servers from Lenovo, Gigabyte and other vendors contains some potentially serious vulnerabilities.
The BMC is a small computer present on a majority of server motherboards. A component of the Intelligent Platform Management Interface (IPMI), it allows administrators to remotely control and monitor a server without having to access the operating system or applications running on it. Admins can use the BMC to reboot a device, install an operating system, update the firmware, monitor system parameters, and analyze logs.
While the capabilities provided by the BMC can be highly useful, the system also introduces security risks, with several attacks demonstrated in the past by experts.
Eclypsium researchers discovered flaws in the BMC firmware while analyzing a Lenovo ThinkServer RD340 server. Further analysis revealed that the vulnerable firmware was sourced as a third-party product called MergePoint EMS, made by Vertiv (formerly Avocent), which is also used by many Gigabyte Enterprise Servers.
The vulnerabilities also made their way into firmware present on motherboards provided by Gigabyte to other companies for their own servers, including Acer, Amax, Bigtera, Ciara, Penguin Computing and sysGen.
“This highlights an important challenge for the industry. Most hardware vendors do not write their own firmware and instead rely on their supply chain partners,” Eclypsium explained. “Firmware is quite commonly licensed from a third party and used with little modification, allowing vulnerabilities to extend to many different brands and products. To adapt, manufacturers must thoroughly test any firmware they license for vulnerabilities. Likewise, enterprise security teams should perform security scans of device firmware as part of accepting any new piece of hardware.”
Eclypsium researchers have identified two types of BMC firmware vulnerabilities. One of them is related to the fact that the firmware update process does not check an update’s cryptographic signature before accepting it and writing it to the SPI flash memory. The second issue is that the code responsible for the firmware update process contains a vulnerability that can be exploited for command injection.
An attacker who has elevated privileges on the host can exploit these flaws to execute malicious code in the BMC as root and modify the content of the BMC memory. This allows them to maintain persistence across reinstallation of the operating system, and prevent other firmware updates. The only way to recover from these attacks is to physically reflash the SPI chip, Eclypsium says.
“Because IPMI communications can be performed over the BMC LAN interface, this update mechanism could be exploited remotely if the attacker has been able to capture the administration password for the BMC. This is particularly likely in the case of IPMI group managed systems where all members of the group share the same administration credentials,” the company warned.
Lenovo has confirmed the existence of the command injection vulnerability (tracked as CVE-2018-9086) and released patches for impacted ThinkServer servers. Gigabyte has also released a patched firmware version, but only for one of the two affected versions. Vertiv, on the other hand, did not respond to the security firm’s communications.
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