Arch Linux Security Advisory ASA-202004-2

Severity: High
Date : 2020-04-01
CVE-ID : CVE-2020-8835
Package : linux-hardened
Type : privilege escalation
Remote : No
Link : https://security.archlinux.org/AVG-1120

Summary

The package linux-hardened before version 5.5.13.b-1 is vulnerable to
privilege escalation.

Resolution

Upgrade to 5.5.13.b-1.

pacman -Syu “linux-hardened>=5.5.13.b-1”

The problem has been fixed upstream in version 5.5.13.b.

Workaround

By default linux-hardened is safe as it restricts BPF access to
privileged users. In case the kernel.unprivileged_bpf_disabled setting
has been explicitly changed, it can be restricted again:

sysctl -w kernel.unprivileged_bpf_disabled=1

Description

An out-of-bounds access flaw was found in the Linux kernel’s
implementation of the eBPF code verifier, where an incorrect register
bounds calculation while checking 32-bit instructions in an eBPF
program occurs. This flaw allows an unprivileged user or process to
execute eBPF programs to crash the kernel, resulting in a denial of
service or potentially gaining root privileges on the system.

Impact

An unprivileged local user or process can crash the kernel, resulting
in a denial of service, or potentially gain root privileges on the
system in case the default BPF access has been changed to allow
unprivileged users.

References

https://www.thezdi.com/blog/2020/3/19/pwn2own-2020-day-one-results
https://lore.kernel.org/bpf/[email protected]/T/
https://www.openwall.com/lists/oss-security/2020/03/30/3
https://security.archlinux.org/CVE-2020-8835