CVE-2021-44141

A vulnerability was found in Samba due to an insecure link following. By querying a symlink inside the exported share using SMB1 with unix extensions turned on, an attacker can discover if a named or directory exists on the filesystem outside the exported share. This flaw allows a remote authenticated attacker to obtain sensitive information.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Do not enable SMB1 (please note SMB1 is disabled by default in Samba from version 4.11.0 and onwards). This prevents the creation or querying of symbolic links via SMB1. If SMB1 must be enabled for backwards compatibility then add the parameter:

unix extensions = no

to the [global] section of your smb.conf and restart smbd. This prevents SMB1 clients from creating or reading symlinks on the exported file system.

However, if the same region of the file system is also exported allowing write access via NFS, NFS clients can create symlinks that allow SMB1 with unix extensions clients to discover the existance of the NFS created symlink targets. For non-patched versions of Samba we recommend only exporting areas of the file system by either SMB2 or NFS, not both.