#VU51433 Time-of-check Time-of-use (TOCTOU) Race Condition in Linux kernel - CVE-2020-25212

Vulnerability identifier: #VU51433

Vulnerability risk: Low

CVSSv4.0: 5.9 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear]

CVE-ID: CVE-2020-25212

CWE-ID: CWE-367

Exploitation vector: Local

Exploit availability: No

Vulnerable software:
Linux kernel
Operating systems & Components / Operating system

Vendor: Linux Foundation

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, 5.8.3

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

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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.