Bubblewrap (bwrap) before version 0.4.1, if installed in setuid mode and the kernel supports unprivileged user namespaces, then the bwrap --userns2 option can be used to make the setuid process keep running as root while being traceable. This can in turn be used to gain root permissions. Note that this only affects the combination of bubblewrap in setuid mode (which is typically used when unprivileged user namespaces are not supported) and the support of unprivileged user namespaces. Known to be affected are: Debian testing/unstable, if unprivileged user namespaces enabled (not default) Debian buster-backports, if unprivileged user namespaces enabled (not default) Arch if using linux-hardened, if unprivileged user namespaces enabled (not default) Centos 7 flatpak COPR, if unprivileged user namespaces enabled (not default) This has been fixed in the 0.4.1 release, and all affected users should update.

bubblewrap.c in Bubblewrap before 0.3.3 misuses temporary directories in /tmp as a mount point. In some particular configurations (related to XDGRUNTIMEDIR), a local attacker may abuse this flaw to prevent other users from executing bubblewrap or potentially execute code.

When executing a program via the bubblewrap sandbox, the nonpriv session can escape to the parent session by using the TIOCSTI ioctl to push characters into the terminal's input buffer, allowing an attacker to escape the sandbox.

References:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=850702

Upstream bugs:

https://github.com/projectatomic/bubblewrap/issues/142 https://github.com/projectatomic/bubblewrap/pull/143

Upstream patch:

https://github.com/projectatomic/bubblewrap/commit/d7fc532c42f0e9bf427923bab85433282b3e5117