ngx_cache_purge before 3.0.4 can allow file deletion via a symlink attack in certain situations where nginx and a served application (e.g., WordPress) run under the same user account. The attacker must be able to create a symlink inside the cache path. Version 3.0.4 fixes this for the case of a symlink created at an arbitrary earlier time, but does not resolve an applicable TOCTOU race condition. (The ngx_cache_purge module follows symlinks while walking the cache directory tree during purge operations.
The module relies on nginx's ngx_walk_tree(), which relies on stat() and therefore follows symlinks.)
Attack Parameters
Attack Vector
Local
Requires local access
Attack Complexity
High
Difficult to exploit
Privileges Required
Low
Basic privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
None
No data leak
Integrity
Low
Partial data modification
Availability
Low
Partial disruption
CVSS Vector v3.1