ProFTPD before 1.3.5e and 1.3.6 before 1.3.6rc5 controls whether the home directory of a user could contain a symbolic link through the AllowChrootSymlinks configuration option, but checks only the last path component when enforcing AllowChrootSymlinks. Attackers with local access could bypass the AllowChrootSymlinks control by replacing a path component (other than the last one) with a symbolic link. The threat model includes an attacker who is not granted full filesystem access by a hosting provider, but can reconfigure the home directory of an FTP user.
Use CWE-59, Proftpd vendor hub and Proftpd product page to widen CVE-2017-7418 into its surrounding weakness, vendor, and product context.
Compare it with CVE-2019-12815, CVE-2010-20103 and CVE-2020-9273 for nearby disclosures in the same product family.