CVE-2021-44731 Linux privilege escalation bug affects Canonical’s Snap Package Manager

Qualys experts found a new Linux privilege escalation vulnerability, tracked as CVE-2021-44731, in Canonical’s Snap Package Manager.

Canonical’s Snap software packaging and deployment system are affected by multiple vulnerabilities, including a privilege escalation flaw tracked as CVE-2021-44731 (CVSS score 7.8).

Snap is a software packaging and deployment system developed by Canonical for operating systems that use the Linux kernel. The packages, called snaps, and the tool for using them, snapd, work across a range of Linux distributions

The flaws have been discovered by Qualys researchers, the CVE-2021-44731 is the most severe one and is a race condition in the snap-confine’s setup_private_mount() function.

The snap-confine is a program used internally by snapd to construct the execution environment for snap applications. An unprivileged user can trigger the flaw to gain root privileges on the affected host.

“Successful exploitation of this vulnerability allows any unprivileged user to gain root privileges on the vulnerable host.” reads the post published by the experts. “As soon as the Qualys Research Team confirmed the vulnerability, we engaged in responsible vulnerability disclosure and coordinated with both vendor and open-source distributions in announcing this newly discovered vulnerability.”

Qualys experts also developed a PoC exploit for this issue that allows obtaining full root privileges on default Ubuntu installations.

Below is the full list of vulnerabilities discovered by the experts:

CVE	Description
CVE-2021-44731	Race condition in snap-confine’s setup_private_mount()
CVE-2021-44730	Hardlink attack in snap-confine’s sc_open_snapd_tool()
CVE-2021-3996	Unauthorized unmount in util-linux’s libmount
CVE-2021-3995	Unauthorized unmount in util-linux’s libmount
CVE-2021-3998	Unexpected return value from glibc’s realpath()
CVE-2021-3999	Off-by-one buffer overflow/underflow in glibc’s getcwd()
CVE-2021-3997	Uncontrolled recursion in systemd’s systemd-tmpfiles

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Pierluigi Paganini

(SecurityAffairs – hacking, CVE-2021-44731)

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