An issue was discovered in the Linux kernel 4.18 through 5.6.11 when unprivileged user namespaces are allowed. A user can create their own PID namespace, and mount a FUSE filesystem. Upon interaction with this FUSE filesystem, if the userspace component is terminated via a kill of the PID namespace's pid 1, it will result in a hung task, and resources being permanently locked up until system reboot. This can result in resource exhaustion.

References

• https://nvd.nist.gov/vuln/detail/CVE-2019-20794
• https://github.com/sargun/fuse-example
• http://www.openwall.com/lists/oss-security/2020/08/24/1
• https://security.netapp.com/advisory/ntap-20200608-0001
• https://sourceforge.net/p/fuse/mailman/message/36598753