[…] The vulnerabilities reside inside firmware that Duluth, Georgia-based AMI makes for BMCs (baseboard management controllers). These tiny computers soldered into the motherboard of servers allow cloud centers, and sometimes their customers, to streamline the remote management of vast fleets of computers. They enable administrators to remotely reinstall OSes, install and uninstall apps, and control just about every other aspect of the system—even when it’s turned off. BMCs provide what’s known in the industry as “lights-out” system management.
These vulnerabilities range in severity from High to Critical, including unauthenticated remote code execution and unauthorized device access with superuser permissions. They can be exploited by remote attackers having access to Redfish remote management interfaces, or from a compromised host operating system. Redfish is the successor to traditional IPMI and provides an API standard for the management of a server’s infrastructure and other infrastructure supporting modern data centers. Redfish is supported by virtually all major server and infrastructure vendors, as well as the OpenBMC firmware project often used in modern hyperscale environments.
The researchers went on to note that if they could locate the vulnerabilities and write exploits after analyzing the publicly available source code, there’s nothing stopping malicious actors from doing the same. And even without access to the source code, the vulnerabilities could still be identified by decompiling BMC firmware images. There’s no indication malicious parties have done so, but there’s also no way to know they haven’t.
The researchers privately notified AMI of the vulnerabilities, and the company created firmware patches, which are available to customers through a restricted support page. AMI has also published an advisory here.
The vulnerabilities are:
- CVE-2023-34329, an authentication bypass via HTTP headers that has a severity rating of 9.9 out of 10, and
- CVE-2023-34330, Code injection via Dynamic Redfish Extension. Its severity rating is 8.2.
“By spoofing certain HTTP headers, an attacker can trick BMC into believing that external communication is coming in from the USB0 internal interface,” the researchers wrote. “When this is combined on a system shipped with the No Auth option configured, the attacker can bypass authentication, and perform Redfish API actions.”
One example would be to create an account that poses as a legitimate administrator and has all system rights afforded one.
CVE-2023-34330, meanwhile, can be exploited on systems with the no auth setting to effectively execute code of their choice. In the event the no auth option isn’t enabled, the attackers first must have BMC credentials. That’s a higher bar but by no means out of reach for sophisticated actors.
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