CVE-2019-14821

Published: 1 October 2019

An out-of-bounds access issue was found in the Linux kernel, all versions through 5.3, in the way Linux kernel's KVM hypervisor implements the Coalesced MMIO write operation. It operates on an MMIO ring buffer 'struct kvm_coalesced_mmio' object, wherein write indices 'ring->first' and 'ring->last' value could be supplied by a host user-space process. An unprivileged host user or process with access to '/dev/kvm' device could use this flaw to crash the host kernel, resulting in a denial of service or potentially escalating privileges on the system.

From the Ubuntu Security Team

Matt Delco discovered that the KVM hypervisor implementation in the Linux kernel did not properly perform bounds checking when handling coalesced MMIO write operations. A local attacker with write access to /dev/kvm could use this to cause a denial of service (system crash).

Notes

An attacker needs write access to the /dev/kvm device file to exploit
this flaw. By default, Ubuntu users don't have privileges to write to
/dev/kvm. This is true even when libvirt is installed and in use.

Mitigation

Ensure that untrusted users cannot write to the /dev/kvm device

Status

Severity score breakdown

References

• https://www.openwall.com/lists/oss-security/2019/09/20/1
• https://ubuntu.com/security/notices/USN-4157-1
• https://ubuntu.com/security/notices/USN-4162-1
• https://ubuntu.com/security/notices/USN-4163-1
• https://ubuntu.com/security/notices/USN-4157-2
• https://ubuntu.com/security/notices/USN-4162-2
• https://ubuntu.com/security/notices/USN-4163-2
• https://www.cve.org/CVERecord?id=CVE-2019-14821
• NVD
• Launchpad
• Debian

Bugs

• https://bugzilla.redhat.com/show_bug.cgi?id=1746708