Load Value Injection: Intel CPUs Vulnerable to Reverse Meltdown Attack
Many processors made by Intel are vulnerable to a newly disclosed type of attack named Load Value Injection (LVI), but the chip maker has told customers that the attack is not very practical in real world environments.
The vulnerability, tracked as CVE-2020-0551, was first reported to Intel in April 2019 by Jo Van Bulck from the KU Leuven research university in Belgium and it was analyzed by a team from universities in the United States, Austria and Australia, including some of the researchers who first discovered the Meltdown and Spectre vulnerabilities. A variation of the LVI attack, dubbed Load Value Injection in the Line Fill Buffers (LVI-LFB), was also reported to Intel by researchers at Bitdefender.
The LVI attack, described as a reverse Meltdown-type attack, allows malicious software installed on a device to gain access to potentially sensitive information. Michael Schwarz, one of the several Graz University of Technology researchers involved in the analysis of LVI, told SecurityWeek that remote exploitation of the vulnerability over the internet or the network is not possible.
The university researchers have also demonstrated that LVI attacks can be launched against Intel’s Software Guard Extensions (SGX), which allows developers to isolate application code and data in memory by leveraging hardware encryption.
“Being essentially a ‘reverse Meltdown’-type attack, LVI for the first time combines Spectre-style code gadgets in the victim domain with Meltdown-type microarchitectural data leakage from faulting or assisted load instructions to compose highly innovative and dangerous attacks that allow to directly inject attacker-controlled data into a victim’s transient execution,” researchers explained.
Bitdefender has pointed out that the LVI attack can be particularly problematic in multi-tenant and multi-workload environments, where hardware is shared. In this scenario, an attacker can use a lesser-privileged process they control to speculatively hijack a process with higher privileges.
“The most straightforward risk is the theft of secret data which should otherwise be kept private by security boundaries at the hardware, hypervisor, and operating system levels,” Bitdefender researchers explained. “This information can include anything from encryption keys, to passwords, or other information which an attacker could exfiltrate, or use to gain further control of a targeted system.”
The university researchers pointed out that attacks on Intel SGX require root privileges, but attacks on kernel and other userspace applications can be mounted by an unprivileged attacker. On the other hand, attacks that do not require elevated permissions are more difficult to mount.
Intel says at least one version of the attack works against its Xeon, Core and some Atom processors. The company noted that an attack is not easy to carry out in real world scenarios, but it has released both updates and mitigation advice to address the risks posed by LVI.
“Due to the numerous complex requirements that must be satisfied to successfully carry out, Intel does not believe LVI is a practical method in real world environments where the OS and VMM are trusted,” Intel told SecurityWeek. “New mitigation guidance and tools for LVI are available now and work in conjunction with previously released mitigations to substantively reduce the overall attack surface.”
Part of the LVI attack that is not specific to Intel chips has also been reported to ARM and IBM. Schwarz told SecurityWeek that while they have not specifically analyzed IBM or ARM processors, they are assuming that CPUs affected by Meltdown are also impacted by LVI.
The researchers noted in their paper that while LVI attacks can be more difficult to carry out compared to other Meltdown-style attacks, the new method shows that “Meltdown-type incorrect transient forwarding effects are not as easy to fix as expected.”
Here are some resources for the LVI attack. The university researchers said proof-of-concept (PoC) code will be made available at a later time, but Bitdefender has already released a PoC.