CVE-2020-8835 : What You Need to Know

In the Linux kernel 5.5.0 and newer, a vulnerability in the bpf verifier could lead to out-of-bounds reads and writes in kernel memory. This issue affects versions 5.6-stable, 5.5-stable, and 5.4-stable starting from v5.4.7.

Understanding CVE-2020-8835

This CVE involves a vulnerability in the bpf verifier component of the Linux kernel, impacting various stable versions.

What is CVE-2020-8835?

The bpf verifier in the Linux kernel did not properly restrict register bounds for 32-bit operations, resulting in memory corruption.

The Impact of CVE-2020-8835

The vulnerability could allow an attacker to perform out-of-bounds reads and writes in the kernel memory, potentially leading to privilege escalation or denial of service.

Technical Details of CVE-2020-8835

The technical aspects of the vulnerability in the Linux kernel.

Vulnerability Description

The bpf verifier in Linux kernel versions 5.5.0 and newer did not adequately limit register bounds for 32-bit operations, enabling unauthorized memory access.

Affected Systems and Versions

Linux kernel 5.6-stable (version less than 5.6.1)
Linux kernel 5.5-stable (version less than 5.5.14)
Linux kernel 5.4-stable (version less than 5.4.29)

Exploitation Mechanism

The vulnerability allows attackers to exploit the bpf verifier to perform out-of-bounds reads and writes in the kernel memory, potentially leading to system compromise.

Mitigation and Prevention

Measures to address and prevent the CVE-2020-8835 vulnerability.

Immediate Steps to Take

Set the kernel.unprivileged_bpf_disabled sysctl to 1
Utilize secure boot with the kernel lockdown feature to block BPF program loading

Long-Term Security Practices

Regularly update the Linux kernel to patched versions
Implement strict access controls and monitoring mechanisms

Patching and Updates

Revert commit 581738a681b6 to address the vulnerability in the bpf verifier component of the Linux kernel.