The adm-zip library applies Unix permission bits stored in ZIP entries directly to extracted files when the keepOriginalPermission=true flag is used during extraction. The library reads the mode from the ZIP external attributes and applies it without filtering out special bits such as setuid (0o4000), setgid (0o2000), and sticky bit (0o1000). This allows an attacker to craft a ZIP archive containing files with malicious setuid bits. When extracted as root, these files become root-owned setuid binaries, which can be executed later by less privileged users to escalate privileges. The vulnerability affects adm-zip versions before 0.6.1 and is classified under CWE-732 (incorrect permission assignment).

An attacker who can supply a malicious ZIP archive to a system that extracts it as root with keepOriginalPermission=true can create root-owned setuid files. These files can be executed by unprivileged users to run code with root privileges, resulting in local privilege escalation. The vulnerability is relevant in environments such as Docker builds, CI pipelines, and privileged install steps where root extraction with permission preservation is common. Default extraction without the flag or extraction by non-root users does not lead to privilege escalation.

A fix is available in adm-zip version 0.6.1 and later that masks out special permission bits before applying them to extracted files. Users should upgrade to adm-zip >=0.6.1 to remediate this vulnerability. If upgrading is not immediately possible, avoid using keepOriginalPermission=true when extracting ZIP files from untrusted sources, especially when running as root.