{"id":"CVE-2026-41140","aliases":["GHSA-73h3-mf4w-8647","PYSEC-2026-2890"],"url":"https://o3.security/vulnerability/CVE-2026-41140","summary":"Poetry: Path traversal in tar extraction on Python 3.10.0 - 3.10.12 and 3.11.0 - 3.11.4","details":"### Summary\n\nThe `extractall()` function in `src/poetry/utils/helpers.py:410-426` extracts sdist tarballs without path traversal protection on Python versions where `tarfile.data_filter` is unavailable. Considering only Python versions which are still supported by Poetry, these are 3.10.0 - 3.10.12 and 3.11.0 - 3.11.4.\n\n### Impact\n\nArbitrary file write (path traversal) from untrusted sdist content.\n\n**In practice, the impact is low** because an attacker who exploits this vulnerability can as well include arbitrary code in a `setup.py`, which will be executed when the sdist is built after tar extraction. In other words, a malicious sdist can write arbitrary files by design. However, since it is unexpected and not by design that the file write already happens during tar extraction, this is still considered a vulnerability.\n\nOn Python 3.11.2 (Debian Bookworm default, directly tested), a crafted sdist with `../../` tar member paths writes files outside the intended extraction directory. The traversal occurs during metadata resolution (`poetry add --lock`), before the build backend is run.\n\nAffected Environments: \n- **Python 3.10.0 through 3.10.12** (inclusive): `tarfile.data_filter` absent or broken\n- **Python 3.11.0 through 3.11.4** (inclusive): `tarfile.data_filter` absent or broken\n- **Debian Bookworm**: Python 3.11.2 (default)\n- **Ubuntu 22.04 LTS**: Python 3.10.6 (default)\n\n### Patches\n\nVersions 2.3.4 and newer of Poetry ensure that paths are inside the target directory.\n\n### Root Cause\n\nFile: `src/poetry/utils/helpers.py`, lines 410-426:\n\n```python\ndef extractall(source: Path, dest: Path, zip: bool) -> None:\n    \"\"\"Extract all members from either a zip or tar archive.\"\"\"\n    if zip:\n        with zipfile.ZipFile(source) as archive:\n            archive.extractall(dest)\n    else:\n        broken_tarfile_filter = {(3, 9, 17), (3, 10, 12), (3, 11, 4)}\n        with tarfile.open(source) as archive:\n            if (\n                hasattr(tarfile, \"data_filter\")\n                and sys.version_info[:3] not in broken_tarfile_filter\n            ):\n                archive.extractall(dest, filter=\"data\")\n            else:\n                archive.extractall(dest)  # <-- NO FILTER: path traversal\n```\n\nOn Python versions without a working `tarfile.data_filter`, the `else` branch at line 426 calls `tarfile.extractall()` without any filter or path validation. This enables three attack vectors:\n\n1. **Direct path traversal**: Tar members with `../../` path components write files outside the extraction directory.\n2. **Symlink traversal**: A symlink member pointing outside dest, followed by a file written through that symlink, escapes the boundary.\n3. **Hardlink attacks**: Hardlink members can read arbitrary files (same inode) or overwrite targets outside dest.\n\n#### Call Sites\n\nThis function is called from two locations:\n\n1. **`src/poetry/installation/chef.py:104`** (`_prepare_sdist`): During `poetry install` / `poetry add` when building a package from sdist. Only triggered when the executor is enabled (actual installation).\n\n2. **`src/poetry/inspection/info.py:322`** (`_from_sdist_file`): During dependency resolution (`poetry lock` / `poetry add`). This path is reached when the sdist's `PKG-INFO` lacks `Requires-Dist` metadata, forcing Poetry to extract the archive (and afterwards build the package).\n\n### Suggested Fix\n\nApply path validation in the `else` branch, covering direct traversal, symlinks, and hardlinks:\n\n```python\ndef extractall(source: Path, dest: Path, zip: bool) -> None:\n    \"\"\"Extract all members from either a zip or tar archive.\"\"\"\n    if zip:\n        with zipfile.ZipFile(source) as archive:\n            archive.extractall(dest)\n    else:\n        broken_tarfile_filter = {(3, 9, 17), (3, 10, 12), (3, 11, 4)}\n        with tarfile.open(source) as archive:\n            if (\n                hasattr(tarfile, \"data_filter\")\n                and sys.version_info[:3] not in broken_tarfile_filter\n            ):\n                archive.extractall(dest, filter=\"data\")\n            else:\n                # Validate all member paths before extraction\n                dest_resolved = dest.resolve()\n                safe_members = []\n                for member in archive.getmembers():\n                    member_path = (dest_resolved / member.name).resolve()\n                    if not member_path.is_relative_to(dest_resolved):\n                        raise ValueError(\n                            f\"Refusing to extract {member.name}: \"\n                            f\"would write outside {dest}\"\n                        )\n                    if member.issym():\n                        link_target = (member_path.parent / member.linkname).resolve()\n                        if not link_target.is_relative_to(dest_resolved):\n                            raise ValueError(\n                                f\"Refusing symlink {member.name}: \"\n                                f\"target {member.linkname} outside {dest}\"\n                            )\n                    elif member.islnk():\n                        link_target = (dest_resolved / member.linkname).resolve()\n                        if not link_target.is_relative_to(dest_resolved):\n                            raise ValueError(\n                                f\"Refusing hardlink {member.name}: \"\n                                f\"target {member.linkname} outside {dest}\"\n                            )\n                    safe_members.append(member)\n                archive.extractall(dest, members=safe_members)\n```","published":"2026-04-24T17:10:33.869Z","modified":"2026-10-28T02:31:01.858978460Z","cvss":null,"epss":{"score":0.00294,"percentile":0.21773,"asOf":"2026-08-13"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"poetry","fixedVersion":"2.3.4"}],"fix":null,"references":[{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-41140.json"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:24866"},{"type":"ADVISORY","url":"https://access.redhat.com/security/cve/CVE-2026-41140"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/41xxx/CVE-2026-41140.json"},{"type":"ADVISORY","url":"https://github.com/python-poetry/poetry/security/advisories/GHSA-73h3-mf4w-8647"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-41140"},{"type":"REPORT","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2461604"},{"type":"PACKAGE","url":"https://github.com/python-poetry/poetry"},{"type":"WEB","url":"https://github.com/python-poetry/poetry/releases/tag/2.3.4"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:31:01.858978460Z"}}