Fix symlink path traversal in skill cache extraction

`_safe_extractall` in `crewai.experimental.skills.cache` (the Python < 3.12
fallback used by `SkillCacheManager.store` to unpack registry-downloaded skill
tarballs into `~/.crewai/skills/`) validated each member's *name* against the
destination but never validated symlink/hardlink *targets*. A malicious skill
archive could plant a symlink escaping the destination (e.g.
`link -> /home/user/.ssh`) followed by a regular member written through it
(`link/authorized_keys`), escaping `dest` even though every member name
resolves inside it — the classic symlink-extraction traversal.

This is the same bug fixed in 32d2da1 for the CLI's `_safe_extractall`
(`crewai_cli.experimental.skills.main`); the duplicate copy in the core
library's skill cache was missed. The 3.12+ path
(`extractall(..., filter="data")`) already blocks this; the fallback now
mirrors it by rejecting absolute link targets and any link target that
resolves outside the destination directory.

Adds regression tests covering absolute and relative escaping symlinks plus
benign in-tree symlinks and ordinary archives.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/crewai/src/crewai/experimental/skills/cache.py

@@ -9,6 +9,7 @@ from __future__ import annotations
 from datetime import datetime, timezone
 import json
 import logging
+import os
 from pathlib import Path
 import tarfile
 from typing import TypedDict
@@ -127,12 +128,38 @@ class SkillCacheManager:
 
 
 def _safe_extractall(tf: tarfile.TarFile, dest: Path) -> None:
-    """Path-traversal-safe extraction for Python < 3.12."""
+    """Path-traversal-safe extraction for Python < 3.12.
+
+    Validates both the member's own path and, for symlink/hardlink members,
+    the link target. Without the link-target check a malicious archive can
+    plant a symlink that escapes ``dest`` (e.g. ``link -> /home/user/.ssh``)
+    followed by a regular member written *through* that link
+    (``link/authorized_keys``), escaping ``dest`` even though every member
+    name resolves inside it. This mirrors the protection that
+    ``tarfile.extractall(..., filter="data")`` provides on Python >= 3.12.
+    """
     dest_resolved = dest.resolve()
     for member in tf.getmembers():
         member_path = (dest / member.name).resolve()
         if not member_path.is_relative_to(dest_resolved):
             raise ValueError(f"Blocked path traversal attempt: {member.name!r}")
+        if member.issym() or member.islnk():
+            link_target = member.linkname
+            # Absolute link targets always escape the destination.
+            if os.path.isabs(link_target):
+                raise ValueError(
+                    f"Blocked link target escaping destination: "
+                    f"{member.name!r} -> {link_target!r}"
+                )
+            # Hardlink names are relative to the archive root; symlink
+            # targets are relative to the member's own directory.
+            anchor = dest if member.islnk() else (dest / member.name).parent
+            resolved_target = (anchor / link_target).resolve()
+            if not resolved_target.is_relative_to(dest_resolved):
+                raise ValueError(
+                    f"Blocked link target escaping destination: "
+                    f"{member.name!r} -> {link_target!r}"
+                )
     tf.extractall(dest)  # noqa: S202
 
 

lib/crewai/tests/experimental/skills/test_cache_safe_extract.py

@@ -0,0 +1,108 @@
+"""Regression tests for path-traversal-safe archive extraction in the cache.
+
+Guards against symlink/hardlink-based path traversal in the Python < 3.12
+extraction fallback (`_safe_extractall`) used by `SkillCacheManager.store`.
+The 3.12+ path relies on `tarfile.extractall(..., filter="data")`; the
+fallback must provide the same protection by validating link targets, not
+just member names.
+"""
+
+from __future__ import annotations
+
+import io
+import tarfile
+from pathlib import Path
+
+import pytest
+
+from crewai.experimental.skills.cache import _safe_extractall
+
+
+def _tar_from_members(build) -> tarfile.TarFile:
+    """Build an in-memory tar archive via `build(tf)` and return it for reading."""
+    buf = io.BytesIO()
+    with tarfile.open(fileobj=buf, mode="w") as tf:
+        build(tf)
+    buf.seek(0)
+    return tarfile.open(fileobj=buf, mode="r")
+
+
+def test_blocks_symlink_escaping_destination(tmp_path: Path) -> None:
+    """A symlink whose target escapes dest, plus a file written through it,
+    must be rejected before anything is extracted."""
+    outside = tmp_path / "outside"
+    outside.mkdir()
+    dest = tmp_path / "dest"
+    dest.mkdir()
+
+    def build(tf: tarfile.TarFile) -> None:
+        link = tarfile.TarInfo("link")
+        link.type = tarfile.SYMTYPE
+        link.linkname = str(outside)  # absolute path outside dest
+        tf.addfile(link)
+        payload = b"pwned"
+        info = tarfile.TarInfo("link/evil.txt")
+        info.size = len(payload)
+        tf.addfile(info, io.BytesIO(payload))
+
+    with _tar_from_members(build) as tf:
+        with pytest.raises(ValueError, match="escaping destination"):
+            _safe_extractall(tf, dest)
+
+    assert not (outside / "evil.txt").exists()
+
+
+def test_blocks_relative_symlink_escaping_destination(tmp_path: Path) -> None:
+    """A relative symlink (../..) that escapes dest is also rejected."""
+    dest = tmp_path / "dest"
+    dest.mkdir()
+
+    def build(tf: tarfile.TarFile) -> None:
+        link = tarfile.TarInfo("sub/link")
+        link.type = tarfile.SYMTYPE
+        link.linkname = "../../outside"  # escapes dest from sub/
+        tf.addfile(link)
+
+    with _tar_from_members(build) as tf:
+        with pytest.raises(ValueError, match="escaping destination"):
+            _safe_extractall(tf, dest)
+
+
+def test_allows_benign_relative_symlink(tmp_path: Path) -> None:
+    """A symlink that stays within dest is permitted."""
+    dest = tmp_path / "dest"
+    dest.mkdir()
+
+    def build(tf: tarfile.TarFile) -> None:
+        payload = b"hi"
+        info = tarfile.TarInfo("real.txt")
+        info.size = len(payload)
+        tf.addfile(info, io.BytesIO(payload))
+        link = tarfile.TarInfo("alias.txt")
+        link.type = tarfile.SYMTYPE
+        link.linkname = "real.txt"  # stays inside dest
+        tf.addfile(link)
+
+    with _tar_from_members(build) as tf:
+        _safe_extractall(tf, dest)
+
+    assert (dest / "real.txt").read_bytes() == b"hi"
+
+
+def test_allows_benign_archive(tmp_path: Path) -> None:
+    """An ordinary archive of regular files extracts correctly."""
+    dest = tmp_path / "dest"
+    dest.mkdir()
+
+    def build(tf: tarfile.TarFile) -> None:
+        for name, body in (("SKILL.md", b"# skill"), ("scripts/run.py", b"print(1)")):
+            payload = body
+            info = tarfile.TarInfo(name)
+            info.size = len(payload)
+            tf.addfile(info, io.BytesIO(payload))
+
+    with _tar_from_members(build) as tf:
+        _safe_extractall(tf, dest)
+
+    assert (dest / "SKILL.md").read_bytes() == b"# skill"
+    assert (dest / "scripts" / "run.py").read_bytes() == b"print(1)"