Privilege escalation in NFS client in Linux kernel

1) Time-of-check Time-of-use (TOCTOU) Race Condition

EUVDB-ID: #VU51433

Risk: Low

CVSSv3.1: 6.8 [CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C]

CVE-ID: CVE-2020-25212

CWE-ID: CWE-367 - Time-of-check Time-of-use (TOCTOU) Race Condition

Exploit availability: No

Description

The vulnerability allows a local user to escalate privileges on the system.

The vulnerability exists due to a TOCTOU mismatch in the NFS client code in the Linux kernel. A local user can run a specially crafted program to trigger memory corruption and execute arbitrary code on the system with elevated privileges.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

Linux kernel: before 5.8.3

External links

http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00021.html
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00035.html
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00042.html
http://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.8.3
http://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b4487b93545214a9db8cbf32e86411677b0cca21
http://lists.debian.org/debian-lts-announce/2020/09/msg00025.html
http://lists.debian.org/debian-lts-announce/2020/10/msg00032.html
http://lists.debian.org/debian-lts-announce/2020/10/msg00034.html
http://twitter.com/grsecurity/status/1303370421958578179
http://usn.ubuntu.com/4525-1/
http://usn.ubuntu.com/4527-1/
http://usn.ubuntu.com/4578-1/

Q & A

Can this vulnerability be exploited remotely?

No. This vulnerability can be exploited locally. The attacker should have authentication credentials and successfully authenticate on the system.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.