CVE-2018-20856 Use after free in n/a

High 7.8 Published 26 Jul 2019 Updated 5 Aug 2024

A use-after-free in the Linux kernel block layer allows local attackers to execute arbitrary code or escalate privileges.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2018-20856?

CVE-2018-20856 is a high-severity use after free vulnerability in Linux kernel, published on 26 Jul 2019. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

An issue was discovered in the Linux kernel before 4.18.7. In block/blk-core.c, there is an __blk_drain_queue() use-after-free because a certain error case is mishandled.

Weakness: CWE-416

Which versions are affected by CVE-2018-20856?

It affects 1 product.

Linux distribution packages (10)

`kpatch-patch-3_10_0-957_35_1` Red Hat:rhel_eus:7.6::server	All versions	`0:1-6.el7`
`kpatch-patch-3_10_0-957_35_1-debuginfo` Red Hat:rhel_eus:7.6::server	All versions	`0:1-6.el7`
`kpatch-patch-3_10_0-957_35_2` Red Hat:rhel_eus:7.6::server	All versions	`0:1-5.el7`
`kpatch-patch-3_10_0-957_35_2-debuginfo` Red Hat:rhel_eus:7.6::server	All versions	`0:1-5.el7`
`kpatch-patch-3_10_0-957_38_1` Red Hat:rhel_eus:7.6::server	All versions	`0:1-4.el7`
`kpatch-patch-3_10_0-957_38_1-debuginfo` Red Hat:rhel_eus:7.6::server	All versions	`0:1-4.el7`
`kpatch-patch-3_10_0-957_38_2` Red Hat:rhel_eus:7.6::server	All versions	`0:1-3.el7`
`kpatch-patch-3_10_0-957_38_3` Red Hat:rhel_eus:7.6::server	All versions	`0:1-3.el7`
`kpatch-patch-3_10_0-957_41_1` Red Hat:rhel_eus:7.6::server	All versions	`0:1-1.el7`
`kpatch-patch-3_10_0-957_43_1` Red Hat:rhel_eus:7.6::server	All versions	`0:1-1.el7`

Products include Linux kernel.

How do I fix CVE-2018-20856?

Apply the vendor's patch.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2018-20856 being exploited?

There is no known exploitation of CVE-2018-20856 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as DEBIAN-CVE-2018-20856, GHSA-873h-38h4-56jx, RHSA-2020:0698, UBUNTU-CVE-2018-20856.