PYSEC-2026-1245

### Impact

The default cache strategy uses the basename of a remote schema as the name of the file in the cache, e.g. `https://example.org/schema.json` will be stored as `schema.json`. This naming allows for conflicts. If an attacker can get a user to run `check-jsonschema` against a malicious schema URL, e.g., `https://example.evil.org/schema.json`, they can insert their own schema into the cache and it will be picked up and used instead of the appropriate schema.

Such a cache confusion attack could be used to allow data to pass validation which should have been rejected.

### Patches

A patch is in progress but has not yet been released.

### Workarounds

- Users can use `--no-cache` to disable caching. - Users can use `--cache-filename` to select filenames for use in the cache, or to ensure that other usages do not overwrite the cached schema. (Note: this flag is being deprecated as part of the remediation effort.) - Users can explicitly download the schema before use as a local file, as in `curl -LOs https://example.org/schema.json; check-jsonschema --schemafile ./schema.json`