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

The datamodel-code-generator tool, when processing Protobuf schemas with weak imports, fails to properly validate import paths. Specifically, absolute paths or relative paths containing '..' can escape the designated '__weak_imports__' temporary directory. This allows an attacker supplying a malicious schema to cause the tool to create directories and write files at arbitrary writable locations on the filesystem. The written files contain only a fixed Protobuf syntax declaration line. The vulnerability affects versions >=0.59.0 and <0.81.0. The issue is triggered before the Protobuf compiler runs and requires the victim to run the tool on the attacker-controlled schema. A patch has been merged into the main branch but no official release with the fix is available yet.

An attacker can cause the tool to write files outside the intended temporary directory, potentially creating new directories and overwriting existing writable files. While the file contents are limited and do not allow direct arbitrary code execution, the integrity of files can be compromised. This could disrupt build processes or cause other integrity-related issues. The vulnerability does not impact confidentiality or availability directly but poses a high integrity risk.

A fix has been merged into the main branch of the datamodel-code-generator repository. Users should update to a patched version once it is officially released. Until then, avoid processing untrusted Protobuf schemas with the affected versions (>=0.59.0 <0.81.0). The vendor advisory confirms a patch is available but no release yet. No alternative mitigations are provided.