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.

GNU Bash through 4.3 bash43-026 does not properly parse function definitions in the values of environment variables, which allows remote attackers to execute arbitrary commands via a crafted environment, as demonstrated by vectors involving the ForceCommand feature in OpenSSH sshd, the mod_cgi and mod_cgid modules in the Apache HTTP Server, scripts executed by unspecified DHCP clients, and other situations in which setting the environment occurs across a privilege boundary from Bash execution. NOTE: this vulnerability exists because of an incomplete fix for CVE-2014-6271, CVE-2014-7169, and CVE-2014-6277.

Off-by-one error in the read_token_word function in parse.y in GNU Bash through 4.3 bash43-026 allows remote attackers to cause a denial of service (out-of-bounds array access and application crash) or possibly have unspecified other impact via deeply nested for loops, aka the "word_lineno" issue.

The redirection implementation in parse.y in GNU Bash through 4.3 bash43-026 allows remote attackers to cause a denial of service (out-of-bounds array access and application crash) or possibly have unspecified other impact via crafted use of here documents, aka the "redir_stack" issue.

GNU Bash through 4.3 bash43-026 does not properly parse function definitions in the values of environment variables, which allows remote attackers to execute arbitrary code or cause a denial of service (uninitialized memory access, and untrusted-pointer read and write operations) via a crafted environment, as demonstrated by vectors involving the ForceCommand feature in OpenSSH sshd, the mod_cgi and mod_cgid modules in the Apache HTTP Server, scripts executed by unspecified DHCP clients, and other situations in which setting the environment occurs across a privilege boundary from Bash execution. NOTE: this vulnerability exists because of an incomplete fix for CVE-2014-6271 and CVE-2014-7169.

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.