fix(hg): URL vulnerability via hg

mercurial's aliases make it possible to inject arbitrary commands.
Use `--` to escape them.

> create_repo(
>    url="--config=alias.clone=!touch ./HELLO", vcs="hg", repo_dir="./"
> )

Credit: Alessio Della Libera <alessio.dellalibera@snyk.io> via Snyk

Author: tony

CHANGES

@@ -4,6 +4,12 @@
 
 - _Add your latest changes from PRs here_
 
+### Potential command injection via mercurial URLs
+
+- By setting a mercurial URL with an alias it is possible to execute arbitrary shell commands via
+  `.obtain()` or in the case of uncloned destinations, `.update_repo()`. (#306, credit: Alessio
+  Della Libera)
+
 ### Development
 
 - Run pyupgrade formatting (#305)

libvcs/hg.py

@@ -26,7 +26,9 @@ def __init__(self, url, repo_dir, **kwargs):
     def obtain(self):
         self.ensure_dir()
 
-        self.run(["clone", "--noupdate", "-q", self.url, self.path])
+        # Double hyphens between [OPTION]... -- SOURCE [DEST] prevent command injections
+        # via aliases
+        self.run(["clone", "--noupdate", "-q", "--", self.url, self.path])
         self.run(["update", "-q"])
 
     def get_revision(self):

tests/test_hg.py

@@ -5,7 +5,7 @@
 
 import pytest
 
-from libvcs.shortcuts import create_repo_from_pip_url
+from libvcs.shortcuts import create_repo, create_repo_from_pip_url
 from libvcs.util import run, which
 
 if not which("hg"):
@@ -72,3 +72,28 @@ def test_repo_mercurial(tmp_path: pathlib.Path, repos_path, hg_remote):
     )
 
     assert mercurial_repo.get_revision() == test_repo_revision
+
+
+def test_vulnerability_2022_03_12_command_injection(
+    monkeypatch: pytest.MonkeyPatch,
+    user_path: pathlib.Path,
+    tmp_path: pathlib.Path,
+    hg_remote,
+):
+    """Prevent hg aliases from executed arbitrary commands via URLs.
+
+    As of 0.11 this code path is/was only executed via .obtain(), so this only would
+    effect explicit invocation of .object() or update_repo() of uncloned destination.
+    """
+    random_dir = tmp_path / "random"
+    random_dir.mkdir()
+    monkeypatch.chdir(str(random_dir))
+    mercurial_repo = create_repo(
+        url="--config=alias.clone=!touch ./HELLO", vcs="hg", repo_dir="./"
+    )
+    with pytest.raises(Exception):
+        mercurial_repo.update_repo()
+
+    assert not pathlib.Path(
+        random_dir / "HELLO"
+    ).exists(), "Prevent command injection in hg aliases"