Cr4sh on SMM exploits in Lenovo firmware!

Dmytro Oleksiuk aka Cr4sh has a new blog post on SMM exploits on Lenovo firmware! Very well written and detailed, with source code!

Exploiting SMM callout vulnerabilities in Lenovo firmware
Hi, everyone. In this article I’ll continue to publish my research in PC firmware security field. In previous article, “Breaking UEFI security with software DMA attacks”, I’ve shown how to exploit UEFI boot script table vulnerability and get access to the SMRAM using software DMA attack under Linux. This time we will talk about discovering and exploitation of SMI dispatch vulnerabilities in UEFI System Management Mode drivers. For anyone who’s not familiar with architecture of SMM phase firmware code on UEFI based platforms I’ll strongly recommend to read my other article “Building reliable SMM backdoor for UEFI based platforms”, especially the part about communicating with SMM code using software SMI.

SMM vulnerabilities that I will talk about in this article aren’t new. Around one year ago LegbaCore and Intel Security published two works: “How Many Million BIOSes Would you Like to Infect?” and “A New Class of Vulnerabilities in SMI Handlers” correspondingly, they rediscovered some security issues in SMI handlers code that was actually a known problem among PC firmware developers (for example, same attacks was described in Loïc Duflot work “System Management Mode Design and Security Issues” presented six years ago). Nevertheless, researchers were able to find and report a lot of firmware vulnerabilities of this class in products like Lenovo, Dell, HP laptops and many others (CERT VU#631788). To play with these vulnerabilities I got ThinkPad T450s laptop. According to original security advisory by Lenovo (apparently, it has a lack of technical details) — some unspecified SMM callout vulnerabilities were patched in the latest version of it’s firmware and everything that we need to do is just find out and exploit one of these vulns. […]


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