#VU55143 Integer overflow in Linux kernel - CVE-2021-33909

Vulnerability identifier: #VU55143

Vulnerability risk: Low

CVSSv4.0: 7.1 [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:P/U:Clear]

CVE-ID: CVE-2021-33909

CWE-ID: CWE-190

Exploitation vector: Local

Exploit availability: Yes

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 integer overflow during size_t-to-int conversion when creating, mounting, and deleting a deep directory structure whose total path length exceeds 1GB. An unprivileged local user can write up to 10-byte string to an offset of exactly -2GB-10B below the beginning of a vmalloc()ated kernel buffer.

Successful exploitation of vulnerability may allow an attacker to exploit the our-of-bounds write vulnerability to execute arbitrary code with root privileges.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Linux kernel: before 5.13.4, 5.13.4

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External links
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.13.4
https://github.com/torvalds/linux/commit/8cae8cd89f05f6de223d63e6d15e31c8ba9cf53b
https://www.openwall.com/lists/oss-security/2021/07/20/1

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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. However, proof of concept for this vulnerability is available.