[Suggested description] lxc-user-nic in lxc through 5.0.1 is installed setuid root, and may allow local users to infer whether any file exists, even within a protected directory tree, because "Failed to open" often indicates that a file does not exist, whereas "does not refer to a network namespace path" often indicates that a file exists. NOTE: this is different from CVE-2018-6556 because the CVE-2018-6556 fix design was based on the premise that "we will report back to the user that the open() failed but the user has no way of knowing why it failed"; however, in many realistic cases, there are no plausible reasons for failing except that the file does not exist.

[Additional Information] % ls /l ls: cannot open directory '/l': Permission denied % /usr/lib/x86_64-linux-gnu/lxc/lxc-user-nic delete lol lol /l/h/tt h h
cmd/lxc_user_nic.c: 1096: main: Failed to open "/l/h/tt" <----- file does not exist. % /usr/lib/x86_64-linux-gnu/lxc/lxc-user-nic delete lol lol /l/h/t h h cmd/lxc_user_nic.c: 1101: main: Path "/l/h/t" does not refer to a network namespace path <---- file exist!

liblxc-common is having a SUID binary that can be abused by a regular to know if a file exist or no anywhere in the filesystem, even under directories where only the root user can list files.

[Vulnerability Type] Insecure Permissions

[Vendor of Product] liblxc-common

[Affected Product Code Base] liblxc-common - latest 5.0.1

[Affected Component] /usr/lib/x86_64-linux-gnu/lxc/lxc-user-nic SUID binary.

[Attack Type] Local

[Impact Information Disclosure] true

[Attack Vectors] To exploit the binary liblxc-common should be installed on the system.

[Discoverer] Maher Azzouzi

[Reference] https://github.com/lxc/lxc/blob/0b83d71c2c8f3bac9503f894cd84584f79258bb3/lxc.spec.in#L274 https://github.com/lxc/lxc/blob/0b83d71c2c8f3bac9503f894cd84584f79258bb3/src/lxc/cmd/lxc_user_nic.c#L1085-L1104 https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1783591/comments/45

Use CVE-2022-47952.

CVE-2022-47952

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