art-template's sub-template resolution logic (src/compile/adapter/resolve-filename.js), used by both the include and extend template directives, resolves the target file path via path.resolve(root, filename) with no check afterward that the result remains inside root.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
High
Complete data leak
Integrity
None
No data modification
Availability
None
No disruption
CVSS Vector v3.1