Fix symlink path traversal in skill archive extraction

`_safe_extractall` (the Python < 3.12 fallback used by `crewai skills`
archive unpacking) validated each member's *name* against the destination
but never validated symlink/hardlink *targets*. A malicious skill tarball
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.

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>

Author: theCyberTech

lib/cli/src/crewai_cli/experimental/skills/main.py

@@ -378,12 +378,38 @@ def _read_version(self, skill_md: Path) -> str | None:
 
 
 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/cli/tests/skills/test_safe_extract.py

@@ -0,0 +1,107 @@
+"""Regression tests for path-traversal-safe archive extraction.
+
+Guards against symlink/hardlink-based path traversal in the Python < 3.12
+extraction fallback (`_safe_extractall`). 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_cli.experimental.skills.main 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)"