Apptainer is an open‑source container platform that restricts which directories a container image may be built from via the limit container paths directive in apptainer.conf. In releases before 1.5.1 the directive performs a plain string‑prefix match, so an allowed path such as "/data/safe" also authorizes a sibling path like "/data/safe-but-unsafe". When Apptainer runs with its setuid binary, a local user can therefore launch a container from an unintended directory that lies outside the administrator’s intended allowlist. Installations that do not use setuid mode or that do not configure the limit container paths directive are not affected, and user namespaces already permit users to run containers of their choice.

Apptainer versions before 1.5.1 are affected when the setuid binary is used and the limit container paths directive is enabled. Installations that do not use the setuid binary or that do not specify the limit container paths directive are not vulnerable. Unprivileged containers that run through user namespaces also remain unaffected because they do not rely on this directive.

The CVSS score of 4.8 places this vulnerability in the medium severity range. The EPSS score is reported as < 1% and the issue is not listed in the CISA KEV catalog. The attack vector is local: an attacker who can execute commands on the host and invoke the setuid Apptainer binary can exploit the flaw to run a container from an unintended directory while still exercising the elevated privileges granted to the setuid binary. The fix is to upgrade to version 1.5.1 or later, which implements exact path matching for the limit container paths directive.