Executive brief
crun is a lightweight container runtime used to execute containerized applications. A flaw allows a malicious container to replace /dev/null with a symlink, which after the container is isolated (pivot_root), enables the container process to attach a host file to its stdin/stdout/stderr and change that file's ownership. This could allow an attacker to modify or compromise host system files from within a container.
Technical details
The vulnerability is a link-following flaw (CWE-59) in crun's stdio reopening logic. After pivot_root, crun attempts to reopen /dev/null for stdin/stdout/stderr; if a container has replaced /dev/null with a symlink pointing to a bind-mounted host file, the symlink is followed, attaching the host file to the container's stdio. The attacker can then modify the file's ownership. Attack vector is local with low privilege requirement and high complexity (requires a malicious container image and specific /dev setup). Default configurations mounting a fresh /dev are not vulnerable. No patch is currently available.
Affected products
- containers crun 1.29.1 and earlier
Timeline
- 2026-09-10: disclosed