CVE-2020-27170: 
Linux Kernel vulnerability analysis and mitigation

CVE-2020-27170 was discovered in the Linux kernel before version 5.11.8. The vulnerability exists in kernel/bpf/verifier.c where undesirable out-of-bounds speculation occurs on pointer arithmetic, leading to side-channel attacks that can defeat Spectre mitigations and obtain sensitive information from kernel memory. The issue specifically affects pointer types that do not define a ptr_limit (NVD, OSS Security).

The vulnerability stems from a gap in the Linux kernel's mechanism to mitigate speculatively out-of-bounds loads (Spectre mitigation). Unprivileged BPF programs could perform pointer arithmetic on pointer types not defining ptr_limit, which was not protected against out-of-bounds speculation. This could be exploited through BPF programs attached to sockets, allowing attackers to execute speculatively out-of-bounds loads without restrictions (OSS Security). The CVSS v3.1 base score for this vulnerability is 4.7 (Medium) with vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N (NVD).

The vulnerability allows local unprivileged users to execute side-channel attacks that can extract sensitive information from kernel memory. By bypassing Spectre mitigations, attackers could access contents of kernel memory that should be protected (OSS Security).

The vulnerability was fixed in Linux kernel version 5.11.8 through a series of patches. The primary fix prohibits arithmetic operations for pointer types not defining ptr_limit. Additional hardening patches were also provided to address related issues and improve the security of the affected code. Users should upgrade to kernel version 5.11.8 or later (Kernel Changelog, Git Commit).

Multiple Linux distributions responded to this vulnerability by releasing security updates. Fedora issued updates for versions 32, 33, and 34 to address the vulnerability (Fedora Update). Debian also released security updates for affected versions (Debian Update).