CVE-2020-25211

A flaw was found in the Linux kernel. A local attacker, able to inject conntrack netlink configuration, could overflow a local buffer causing crashes or triggering the use of incorrect protocol numbers in ctnetlink_parse_tuple_filter in net/netfilter/nf_conntrack_netlink.c. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

This flaw is rated as having Moderate impact (Red Hat Enterprise Linux 7 and lower) because of the need to have CAP_NET_ADMIN privileges.

This flaw is rated as having Important (Red Hat Enterprise Linux 8) impact because of the need to have CAP_NET_ADMIN privileges. Red Hat Enterprise Linux 8 enabled unprivileged user/network namespaces by default which can be used to exercise this vulnerability.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, prevent module nf_conntrack_netlink from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.

Alternatively, if nf_conntrack_netlink is being used, on Red Hat Enterprise Linux 8, you can disable unprivileged user namespaces by setting user.max_user_namespaces to 0:

echo "user.max_user_namespaces=0" > /etc/sysctl.d/userns.conf

sysctl -p /etc/sysctl.d/userns.conf