PYSEC-2026-4217 fsspec: Server-Side Template Injection in ReferenceFileSystem leads to Remote Code Execution

Summary fsspec.implementations.reference.ReferenceFileSystem parses a "references" JSON document Kerchunk format supplied either inline or via a URL. The parser renders fields from this JSON through un-sandboxed jinja2.Template....render... calls in three locations. An attacker who controls the...