Tornado before 6.5.9 contains a path traversal vulnerability in StaticFileHandler that follows symbolic links inside the static root without confirming the resolved target stays within it. When a symlink pointing outside the static directory exists inside it, unauthenticated attackers can request it to read files such as configuration files, private keys, and application secrets accessible to the process user.
Weakness
The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.
Potential Mitigations
- Follow the principle of least privilege when assigning access rights to entities in a software system.
- Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/132.html
- https://cwe.mitre.org/data/definitions/17.html
- https://cwe.mitre.org/data/definitions/35.html
- https://cwe.mitre.org/data/definitions/76.html
References
- https://github.com/tornadoweb/tornado/commit/437ab5f76565403b3403438d2e555d11f8128d32
- https://github.com/tornadoweb/tornado/security/advisories/GHSA-c2m8-h5v5-343r
- https://www.vulncheck.com/advisories/tornado-before-6.5.9-staticfilehandler-path-traversal-via-symlink
- https://github.com/tornadoweb/tornado/security/advisories/GHSA-c2m8-h5v5-343r