CVE-2026-107377: datamodel-code-generator: Protobuf weak-import path traversal allows files to be written outside the temporary directory

When processing an attacker-controlled Protobuf schema, vulnerable versions of datamodel-code-generator could write a generated weak-import stub outside the intended __weak_imports__ temporary directory. Absolute import paths and relative paths containing .. could escape this directory.

An attacker could create directories and new files at locations writable by the process. Relative path traversal could also overwrite existing writable files because the existence check and the stub write used different base directories. An existing absolute target was skipped by the existence check.

Written content was limited to a generated Protobuf syntax declaration, syntax = "proto2"; or syntax = "proto3";, followed by a newline. This issue did not provide fully attacker-controlled file contents, and direct arbitrary code execution has not been demonstrated.

These filesystem side effects occurred before protoc ran. A subsequent compilation error did not undo them. A user or CI job must process the attacker-controlled schema for the issue to be triggered, whether the schema is supplied as a local file or fetched via --url.