CVE-2021-25683: 
Linux Ubuntu vulnerability analysis and mitigation

The vulnerability CVE-2021-25683 was discovered in the get_starttime() function in data/apport, which did not properly parse the /proc/pid/stat file from the kernel. This vulnerability was identified on January 19, 2021, and affected Ubuntu's Apport crash reporting system (Ubuntu Bug).

The vulnerability stems from improper parsing of the /proc/pid/stat file in the getprocessstarttime function. The start time is extracted from the 22nd column of the /proc/pid/stat file, but the parsing mechanism could be manipulated by creating a process with a space character in its filename, causing getprocessstarttime to return incorrect values (Ubuntu Bug). The vulnerability has been assigned a CVSS 3 Severity Score of 7.8 (High) (Ubuntu Security).

When exploited, this vulnerability could be chained with other vulnerabilities (CVE-2021-25682 and CVE-2021-25684) to achieve local privilege escalation to root from an unprivileged user. The vulnerability allows attackers to bypass the getprocessstartime check by recycling process IDs with specifically crafted filenames (Ubuntu Bug).

The vulnerability was patched in multiple Ubuntu versions with security updates released on February 2, 2021. Fixes were implemented in apport versions 2.20.11-0ubuntu50.5 (Groovy), 2.20.9-0ubuntu7.23 (Bionic), 2.20.1-0ubuntu2.30 (Xenial), and 2.20.11-0ubuntu27.16 (Focal). The patch included improvements to skip over manipulated process names and filenames, and ensuring existing reports are regular files (Ubuntu Bug).