sh _uid does not drop supplementary groups (incomplete privilege drop)

### Impact The `_uid` option performed an incomplete privilege drop on Linux/Unix-like systems. When `sh` was run from a process with elevated privileges, such as root, and a command was launched with `_uid=<unprivileged user>`, the child process changed its UID and primary GID but did not reset its supplementary groups. As a result, the child process could retain the parent process’s supplementary groups, potentially including privileged groups such as root, docker, disk, shadow, or sudo. This could allow a subprocess that was expected to run with reduced privileges to access files or resources available to the original process’s supplementary groups. Users are impacted if they rely on `_uid` as a privilege boundary when launching commands from a privileged parent process. ### Patches Upgrade to version >= 2.2.4 ### Workarounds Avoid using `_uid` when the user represents a less-privileged user. Source Code Location: https://github.com/amoffat/sh Affected Packages: - pip:sh, affected < 2.2.4, patched in 2.2.4 CWEs: - CWE-273: Improper Check for Dropped Privileges CVSS: - Primary: score 7.9, CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:N - CVSS_V3: score 7.9, CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:N References: - https://github.com/amoffat/sh/security/advisories/GHSA-q38v-wp89-2w55 - https://github.com/amoffat/sh/releases/tag/2.2.4 - https://github.com/advisories/GHSA-q38v-wp89-2w55