A flaw was found in zsh. When unsetting the PRIVILEGED option, the shell sets its effective user and group IDs to match their respective real IDs. When the RUID and EUID were both non-zero, it is possible to regain the shell's former privileges. Also, the setopt built-in did not correctly report errors when unsetting the option, which prevented users from handling them as the documentation recommended. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.