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This vulnerability concerns an incorrect security mitigation in the Linux kernel for ARM64 (arm64) systems. The issue is related to the Branch History Buffer (BHB), a CPU component used for speculative execution. To protect against certain speculation-based attacks (speculative execution), the kernel applies mitigations to BPF programs.
BPF comes in two forms: the older “classic” BPF (cBPF) and the newer “extended” BPF (eBPF). By default, the ability for unprivileged users to load eBPF programs is disabled on most systems. Therefore, the primary attack vector for unprivileged users is through cBPF.
The kernel’s vulnerability was that it applied the BHB mitigation to all cBPF programs indiscriminately. However, this mitigation is only necessary and meaningful for cBPF programs that are loaded by unprivileged users. If a privileged user (like root) loads the exact same cBPF program, they could do so via the eBPF subsystem, which would bypass the applied mitigation, rendering it pointless. The fix ensures the BHB mitigation is applied exclusively to cBPF programs loaded from an unprivileged context, correcting the logic.
Platform: Linux Kernel
Version: Prior to fix
Vulnerability: Improper cBPF mitigation
Severity: Medium
date: 2025-05-20
Prediction: 2025-06-10
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`sysctl -a | grep unprivileged`
`cat /proc/sys/kernel/unprivileged_bpf_disabled`
`grep -i bpf /boot/config-$(uname -r)`
How Exploit:
An unprivileged local attacker could craft and load a cBPF program designed to interact with the CPU’s Branch History Buffer. By exploiting the missing targeted mitigation, they could potentially manipulate speculative execution to access unauthorized data in the kernel’s memory space.
Protection from this CVE
Apply the official kernel patch. Restrict unprivileged user access to the `bpf()` system call via sysctl (kernel.unprivileged_bpf_disabled=1). Update to a Linux kernel version containing the commit that resolves this issue.
Impact:
Potential information disclosure via speculative execution side-channel. The impact is limited to local attackers and relies on specific CPU architectures (arm64) with cBPF usage.
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Reported By: nvd.nist.gov
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