CVE-2026-55389: Datamodel code generator //` And `../` Traversal), Bypassing Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-8359-h9fx-j6v9",
  "modified" : "2026-07-28T21:49:34Z",
  "published" : "2026-07-28T21:49:34Z",
  "aliases" : [ "CVE-2026-55389" ],
  "summary" : "datamodel-code-generator vulnerable to arbitrary local file read via JSON-Schema `$ref` (`file://` and `../` traversal), bypassing `--no-allow-remote-refs`",
  "details" : "### Summary\n\n`datamodel-code-generator` resolves JSON-Schema `$ref` targets that point at the local filesystem without restricting them to the input/base directory and without honoring the remote-reference security control. In the default configuration, an attacker who controls an input schema (a \"paste your OpenAPI/JSON-Schema\" service, a CI job that generates models from a submitted spec, or any multi-tenant codegen platform) can read any file the process user can read and map the host filesystem. This works via either a `file://` absolute URI or a `../`-escaped relative reference, and it succeeds even when `--no-allow-remote-refs` is set.\n\nThis is an unauthenticated path-traversal / information-disclosure issue (CWE-22 / CWE-200) plus a bypass of a documented security control.\n\n### Details\n\n`is_url()` classifies `file://` as a URL (`reference.py:1249`):\n\n```python\ndef is_url(ref: str) -> bool:\n    return ref.startswith((\"https://\", \"http://\", \"file://\"))\n```\n\nThe remote-ref gate then explicitly exempts `file://`, so `--no-allow-remote-refs` never applies to it (`parser/jsonschema.py`, `_get_ref_body`):\n\n```python\nif is_url(resolved_ref):\n    if not resolved_ref.startswith(\"file://\") and self.http_local_ref_path is None:\n        if self.allow_remote_refs is False:\n            raise Error(...)        # <-- skipped for file://\n        ...\n    return self._get_ref_body_from_url(resolved_ref)\nreturn self._get_ref_body_from_remote(resolved_ref)\n```\n\nBoth local-file branches read the target with **no containment check**. The `file://` branch reads any absolute path:\n\n```python\n# _get_ref_body_from_url\nif ref.startswith(\"file://\"):\n    path = url2pathname(urlparse(ref).path)     # absolute path, anywhere on disk\n    return self.remote_object_cache.get_or_put(\n        ref, default_factory=lambda _: load_data_from_path(Path(path), self.encoding))\n```\n\nand the plain relative branch lets `../` escape the base directory:\n\n```python\n# _get_ref_body_from_remote\nfull_path = self.base_path / resolved_ref       # no is_relative_to(base_path) check\nreturn self.remote_object_cache.get_or_put(\n    str(full_path), default_factory=lambda _: load_data_from_path(full_path, self.encoding))\n```\n\nFor contrast, the HTTP-local-ref branch (`_get_ref_body_from_local_http_path`) *does* enforce `is_relative_to(base_path)`; these two filesystem branches do not. (This is distinct from the previously reported HTTP `$ref`/`--url` SSRF hardened in `http.py`  these code paths never enter `http.py`.)\n\nThe fetched file is read and parsed, yielding two impacts:\n\n1. **Arbitrary file read + filesystem oracle (any file).** The process opens any readable path, and the three distinguishable outcomes leak filesystem structure: `Expected dict, got str/list` = the file exists and was read into the process; `FileNotFoundError: '<abs path>'` = missing; `PermissionError: '<abs path>'` = exists but unreadable. An attacker uses this to probe arbitrary paths and recover the operator's absolute filesystem layout.\n\n2. **Verbatim secret disclosure into the generated code.** When the referenced node is JSON-Schema-shaped, values in `const`/`default`/`enum`/`description` positions are emitted verbatim into the generated Python that is returned to the attacker — i.e. exactly the internal/private schema and config files a codegen host stores (specs with example/default tokens, default credentials, internal hostnames, service-account JSON, k8s secret manifests).\n\nScope note (to avoid overstating): the *raw bytes* of unstructured files such as `/etc/passwd` or a PEM `id_rsa` are read into the process but are not echoed verbatim into the output, because they parse to a single scalar and are rejected as \"not a schema\". For those files the impact is the read itself plus the existence/permission/absolute-path oracle; verbatim content disclosure applies to schema-shaped nodes.\n\n### PoC\n\nSelf-contained reproducer: https://gist.github.com/thegr1ffyn/2a87e81f985883acc30d0118c52da4d3 /  (`poc.py` creates everything in a temp dir, runs the generator, asserts read + leak + gate bypass, and cleans up). \nMinimal manual reproduction of the arbitrary read (any path works):\n\n```bash\nprintf '{\"type\":\"object\",\"properties\":{\"x\":{\"$ref\":\"file:///etc/passwd\"}}}' > probe.json\ndatamodel-codegen --input probe.json --input-file-type jsonschema --output o.py\n# -> \"TypeError: Expected dict, got str\"  == /etc/passwd was opened and fully parsed.\n# Swap the $ref for a missing/unreadable path to see the existence/permission oracle.\n```\n\n### Impact\n\nArbitrary local file read / path traversal (CWE-22) → information disclosure (CWE-200), plus bypass of `--no-allow-remote-refs`. Any application, CI pipeline, or multi-tenant service that runs `datamodel-code-generator` on an untrusted schema and exposes (returns, logs, commits, renders) the generated code is affected. The attacker can: open and read any file the process user can read (demonstrated: `/etc/passwd`, a PEM `id_rsa`, paths under `/root/`); map the host filesystem and recover absolute paths; and exfiltrate secret values verbatim from any schema-shaped node. Attacker controls only the input schema; no authentication or special privileges required.\n\n### Suggested remediation\n\n1. Do not exempt `file://` from the `allow_remote_refs` gate, treat it as an external scheme.\n2. In both `_get_ref_body_from_url` (the `file://` case) and `_get_ref_body_from_remote`, reject targets that are not `resolved.is_relative_to(self.base_path)`, mirroring the existing check in `_get_ref_body_from_local_http_path`.\n\n### Maintainer status\n\nConfirmed by maintainer review and regression tests. The private fix PR was merged and released in `0.62.0`: https://github.com/koxudaxi/datamodel-code-generator-ghsa-8359-h9fx-j6v9/pull/1\n\nFix summary: apply the remote-ref gate to `file://` refs and local JSON Schema refs outside the input base path. In `0.62.0`, `--no-allow-remote-refs` blocks these references; the default compatibility mode emits a `FutureWarning` and users who intentionally rely on trusted external local refs can pass `--allow-remote-refs`.\n\nRelease status: fixed in `0.62.0` for the documented `--no-allow-remote-refs` bypass, with a compatibility warning for the default behavior.\n\nValidation: `uv run --group test --extra http pytest tests/main/jsonschema/test_main_jsonschema.py` passed locally; `uv run --group fix ruff check src/datamodel_code_generator/parser/jsonschema.py tests/main/jsonschema/test_main_jsonschema.py` passed.\n\nSubmitted by: Hamza Haroon (thegr1ffyn)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "datamodel-code-generator"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.62.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.61.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/koxudaxi/datamodel-code-generator/security/advisories/GHSA-8359-h9fx-j6v9"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/koxudaxi/datamodel-code-generator/commit/2ff4a72b4550a2b2069754c5b075b1655067e5fb"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/koxudaxi/datamodel-code-generator"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/koxudaxi/datamodel-code-generator/releases/tag/0.62.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-200", "CWE-22", "CWE-610" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-28T21:49:34Z",
    "nvd_published_at" : null
  }
}