Firejail is a SUID security sandbox program that reduces the risk of security breaches by restricting the running environment of untrusted applications using Linux namespaces and seccomp-bpf. Therefore it may span an OverlayFS over the complete file system, redirecting any file system modifications to a temporary space. Thus malicious sandboxed processes cannot change files on the "real" active file system. To create such a sandbox elevated privileges are required.
When setting up the sandbox Firejail tries to ensure, that the location for temporary OverlayFS file root is not writable by any unprivileged user as that may allow privilege escalation. Due to a race condition this check may report a wrong status and thus both follow symbolic links and use an untrusted directory as source. With crafted content using the untrusted directory allows creation of or granting write access to arbitrary files.
Created firejail tracking bugs for this issue:
Affects: fedora-all [bug 1926480]
This CVE Bugzilla entry is for community support informational purposes only as it does not affect a package in a commercially supported Red Hat product. Refer to the dependent bugs for status of those individual community products.