check-jsonschema default caching for remote schemas allows for cache confusion

Summary

check-jsonschema is a CLI and set of pre-commit hooks for jsonschema validation. 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. This issue has been patched in version 0.30.0. All users are advised to upgrade. A few workarounds exist: 1. Users can use `--no-cache` to disable caching. 2. 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.) 3. 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`

Timeline

1. Nov 29, 2024, 6:39 PM UTCCVE published
2. Dec 2, 2024, 10:19 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Dec 2, 2024, 10:20 PM UTCRecord last updated

Affected versions

• python-jsonschema check-jsonschema

  fixed in 0.30.0

• check-jsonschemaPyPI

  fixed in 0.30.0

References 2