Client metadata path-traversal

Impact

In both clients (tuf/client and tuf/ngclient), there is a path traversal vulnerability that in the worst case can overwrite files ending in .json anywhere on the client system on a call to get_one_valid_targetinfo(). It occurs because the rolename is used to form the filename, and may contain path traversal characters (ie ../../name.json).

The impact is mitigated by a few facts:

• It only affects implementations that allow arbitrary rolename selection for delegated targets metadata
• The attack requires the ability to A) insert new metadata for the path-traversing role and B) get the role delegated by an existing targets metadata
• The written file content is heavily restricted since it needs to be a valid, signed targets file. The file extension is always .json.

Patches

A fix is available in version 0.19 or newer.

Workarounds

None that do not require code changes. Clients can restrict the allowed character set for rolenames, or they can store metadata in files named in a way that is not vulnerable: neither of these approaches is possible without modifying python-tuf.

References

• The issue where this was discovered
• Proof of Concept demonstrating the flaw

For more information

If you have any questions or comments about this advisory:

• Open an issue in python-tuf
• Contact the maintainers by email or Slack