An issue was discovered in disable_priv_mode in shell.c in GNU Bash through 5.0 patch 11. By default, if Bash is run with its effective UID not equal to its real UID, it will drop privileges by setting its effective UID to its real UID. However, it does so incorrectly. On Linux and other systems that support "saved UID" functionality, the saved UID is not dropped. An attacker with command execution in the shell can use "enable -f" for runtime loading of a new builtin, which can be a shared object that calls setuid() and therefore regains privileges. However, binaries running with an effective UID of 0 are unaffected.

rbash in Bash before 4.4-beta2 did not prevent the shell user from modifying BASH_CMDS, thus allowing the user to execute any command with the permissions of the shell.

popd in bash might allow local users to bypass the restricted shell and cause a use-after-free via a crafted address.

Bash before 4.4 allows local users to execute arbitrary commands with root privileges via crafted SHELLOPTS and PS4 environment variables.

The prompt parsing in bash allows a local user to execute commands as another user by creating a directory with the name of the command to execute.

(1) bash before 1.14.7, and (2) tcsh 6.05 allow local users to gain privileges via directory names that contain shell metacharacters (` back-tick), which can cause the commands enclosed in the directory name to be executed when the shell expands filenames using the \w option in the PS1 variable.