GHSA-qp9x-wp8f-qgjj

`DelegatedRole._is_target_in_pathpattern` uses `fnmatch.fnmatch` to decide whether a given target path is authorized by a delegation's glob pattern.

Python's `fnmatch.fnmatch` calls `os.path.normcase()` on both arguments before matching. On POSIX hosts `normcase` is the identity function; on Windows hosts `os.path` resolves to `ntpath`, whose `normcase` lowercases its input and replaces `/` with `\`.

As a result, python-tuf's delegation *path pattern* matching is case-sensitive on Linux/macOS but case-INSENSITIVE on Windows. This makes the authorization decision for a target dependent on the host operating system of the client running the updater.

The result on Windows is a TUF specification violation in the python-tuf `ngclient` implementation.

## Vulnerable code

`tuf/api/_payload.py` (HEAD `7ecb67d`):

```python 1183 @staticmethod 1184 def _is_target_in_pathpattern(targetpath: str, pathpattern: str) -> bool: 1185 """Determine whether ``targetpath`` matches the ``pathpattern``.""" 1186 # We need to make sure that targetpath and pathpattern are pointing to 1187 # the same directory as fnmatch doesn't threat "/" as a special symbol. 1188 target_parts = targetpath.split("/") 1189 pattern_parts = pathpattern.split("/") 1190 if len(target_parts) != len(pattern_parts): 1191 return False 1192 1193 # Every part in the pathpattern could include a glob pattern, that's why 1194 # each of the target and pathpattern parts should match. 1195 for target, pattern in zip(target_parts, pattern_parts, strict=True): 1196 if not fnmatch.fnmatch(target, pattern): 1197 return False 1198 return True ```

`fnmatch.fnmatch` source (Python 3.12, unchanged in current mainline):

```python def fnmatch(name, pat): ... name = os.path.normcase(name) pat = os.path.normcase(pat) return fnmatchcase(name, pat) ```

## Fix

Replace `fnmatch.fnmatch` with `fnmatch.fnmatchcase`, which is explicitly documented as "not applying case normalization", so it behaves identically across platforms.

## Attack

1. A TUF repository with two path-based delegations whose patterns differ only in case — for example, `Foo/*` and `foo/*`. 2. The "attacker" delegation is listed BEFORE the "legit" delegation in the delegation order. 3. The client searches for `foo/something`: on Windows, it will find the "attacker" provided target "Foo/something".

## Exploitability caveats

* The attack needs a repository configuration with case-colliding delegation path patterns. The attacker must control one of the delegated roles. * Delegation ordering matters: the attacker-controlled role must be visited BEFORE the legit role in the pre-order walk. * The client must run on Windows. No effect on Linux/macOS.

## Credit

Reporter: Koda Reef @kodareef5 Advisory edits: Jussi Kukkonen @jku