fix(security): consolidated security hardening — SSRF, timing attack, tar traversal, credential leakage (#5944)

Salvaged from PRs #5800 (memosr), #5806 (memosr), #5915 (Ruzzgar), #5928 (Awsh1).

Changes:
- Use hmac.compare_digest for API key comparison (timing attack prevention)
- Apply provider env var blocklist to Docker containers (credential leakage)
- Replace tar.extractall() with safe extraction in TerminalBench2 (CVE-2007-4559)
- Add SSRF protection via is_safe_url to ALL platform adapters:
  base.py (cache_image_from_url, cache_audio_from_url),
  discord, slack, telegram, matrix, mattermost, feishu, wecom
  (Signal and WhatsApp protected via base.py helpers)
- Update tests: mock is_safe_url in Mattermost download tests
- Add security tests for tar extraction (traversal, symlinks, safe files)

environments/benchmarks/terminalbench_2/terminalbench2_env.py

@@ -44,7 +44,7 @@ import tempfile
 import time
 import uuid
 from collections import defaultdict
-from pathlib import Path
+from pathlib import Path, PurePosixPath, PureWindowsPath
 from typing import Any, Dict, List, Optional, Tuple, Union
 
 # Ensure repo root is on sys.path for imports
@@ -148,6 +148,62 @@ MODAL_INCOMPATIBLE_TASKS = {
 # Tar extraction helper
 # =============================================================================
 
+def _normalize_tar_member_parts(member_name: str) -> list:
+    """Return safe path components for a tar member or raise ValueError."""
+    normalized_name = member_name.replace("\\", "/")
+    posix_path = PurePosixPath(normalized_name)
+    windows_path = PureWindowsPath(member_name)
+
+    if (
+        not normalized_name
+        or posix_path.is_absolute()
+        or windows_path.is_absolute()
+        or windows_path.drive
+    ):
+        raise ValueError(f"Unsafe archive member path: {member_name}")
+
+    parts = [part for part in posix_path.parts if part not in ("", ".")]
+    if not parts or any(part == ".." for part in parts):
+        raise ValueError(f"Unsafe archive member path: {member_name}")
+    return parts
+
+
+def _safe_extract_tar(tar: tarfile.TarFile, target_dir: Path) -> None:
+    """Extract a tar archive without allowing traversal or link entries."""
+    target_dir.mkdir(parents=True, exist_ok=True)
+    target_root = target_dir.resolve()
+
+    for member in tar.getmembers():
+        parts = _normalize_tar_member_parts(member.name)
+        target = target_dir.joinpath(*parts)
+        target_real = target.resolve(strict=False)
+
+        try:
+            target_real.relative_to(target_root)
+        except ValueError as exc:
+            raise ValueError(f"Unsafe archive member path: {member.name}") from exc
+
+        if member.isdir():
+            target_real.mkdir(parents=True, exist_ok=True)
+            continue
+
+        if not member.isfile():
+            raise ValueError(f"Unsupported archive member type: {member.name}")
+
+        target_real.parent.mkdir(parents=True, exist_ok=True)
+        extracted = tar.extractfile(member)
+        if extracted is None:
+            raise ValueError(f"Cannot read archive member: {member.name}")
+
+        with extracted, open(target_real, "wb") as dst:
+            shutil.copyfileobj(extracted, dst)
+
+        try:
+            os.chmod(target_real, member.mode & 0o777)
+        except OSError:
+            pass
+
+
 def _extract_base64_tar(b64_data: str, target_dir: Path):
     """Extract a base64-encoded tar.gz archive into target_dir."""
     if not b64_data:
@@ -155,7 +211,7 @@ def _extract_base64_tar(b64_data: str, target_dir: Path):
     raw = base64.b64decode(b64_data)
     buf = io.BytesIO(raw)
     with tarfile.open(fileobj=buf, mode="r:gz") as tar:
-        tar.extractall(path=str(target_dir))
+        _safe_extract_tar(tar, target_dir)
 
 
 # =============================================================================