CVE-2019-19816

A flaw was found in the implementation of the BTRFS file system code in the Linux kernel. An attacker, who is able to mount a crafted BTRFS filesystem and perform common filesystem operations, can possibly cause an out-of-bounds write to memory. This could lead to memory corruption or privilege escalation.

The vulnerability is considered moderate rather than important because it requires specific conditions to be exploited. An attacker must have physical access to the system and be able to mount a crafted BTRFS filesystem, which limits the potential attack vectors and also a local account to abuse the use-after-free. Additionally, the flaw involves an out-of-bounds write when handling RAID56 metadata, which could lead to memory corruption, but exploitation for privilege escalation is not straightforward due to mitigations like kernel address space layout randomization (KASLR). As a result, the impact is more constrained, affecting system stability rather than directly allowing unauthorized access or significant data compromise.

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.

As the BTRFS module will be auto-loaded when required, its use can be disabled by preventing the module from loading with the following instructions:

echo "install btrfs /bin/true" >> /etc/modprobe.d/disable-btrfs.conf

The system will need to be restarted if the BTRFS modules are loaded, it may be possible to unload them. In most circumstances, the BTRFS kernel modules will be unable to be unloaded while any BTRFS filesystems are mounted or in use.

If the system requires this module to work correctly, this mitigation may not be suitable.

If you need further assistance, see KCS article https://access.redhat.com/solutions/41278 or contact Red Hat Global Support Services.