diff --git a/plugins/security-guidance/hooks/_base.py b/plugins/security-guidance/hooks/_base.py
index 7e8eeed5..9adbcff4 100644
--- a/plugins/security-guidance/hooks/_base.py
+++ b/plugins/security-guidance/hooks/_base.py
@@ -10,15 +10,42 @@ import os
 import threading
 from datetime import datetime
 
+def state_dir():
+    """Return the absolute path of the plugin's state directory.
+
+    Resolution precedence (highest first):
+      1. SECURITY_WARNINGS_STATE_DIR — plugin-specific override (existing)
+      2. CLAUDE_CONFIG_DIR/security  — CC's config-dir env var (#1868)
+      3. ~/.claude/security          — default fallback
+
+    Empty-string env vars are treated as not-set so a misconfigured shell
+    (`CLAUDE_CONFIG_DIR=` with no value) doesn't silently write to
+    /security at the filesystem root.
+
+    Returns a fully-expanded absolute path (no literal `~`) so subprocess
+    callers can pass it through to code that doesn't re-expand tildes.
+
+    Called per-invocation rather than cached at import time so test
+    monkeypatches of the env vars take effect — the plugin's hooks each
+    run as fresh subprocesses in production, so the per-call cost is
+    negligible compared to subprocess spawn.
+    """
+    explicit = os.environ.get("SECURITY_WARNINGS_STATE_DIR")
+    if explicit:
+        return os.path.expanduser(explicit)
+    cc_config = os.environ.get("CLAUDE_CONFIG_DIR")
+    if cc_config:
+        return os.path.expanduser(os.path.join(cc_config, "security"))
+    return os.path.expanduser("~/.claude/security")
+
+
 # Debug log file. Lives under the plugin state dir (default ~/.claude/security/)
 # rather than /tmp because /tmp is world-writable on multi-user hosts (TOCTOU /
 # symlink-attack surface, cross-user log leakage). Overridable per-process via
-# SECURITY_GUIDANCE_DEBUG_LOG, or per-state-dir via SECURITY_WARNINGS_STATE_DIR.
-_DEFAULT_STATE_DIR = os.path.expanduser(
-    os.environ.get("SECURITY_WARNINGS_STATE_DIR") or "~/.claude/security"
-)
+# SECURITY_GUIDANCE_DEBUG_LOG, or per-state-dir via SECURITY_WARNINGS_STATE_DIR
+# (plugin-specific override) or CLAUDE_CONFIG_DIR (CC-wide config dir, #1868).
 DEBUG_LOG_FILE = os.environ.get("SECURITY_GUIDANCE_DEBUG_LOG") or os.path.join(
-    _DEFAULT_STATE_DIR, "log.txt"
+    state_dir(), "log.txt"
 )
 # Cap the debug log so parallel-worker fleets don't fill disk. When the active
 # file exceeds this it's atomically rotated to <file>.1 (overwriting any prior
diff --git a/plugins/security-guidance/hooks/ensure_agent_sdk.py b/plugins/security-guidance/hooks/ensure_agent_sdk.py
index 4f7d30b9..262a53a9 100644
--- a/plugins/security-guidance/hooks/ensure_agent_sdk.py
+++ b/plugins/security-guidance/hooks/ensure_agent_sdk.py
@@ -23,6 +23,12 @@ import sys
 import time
 from pathlib import Path
 
+# Shared state-dir resolver: SECURITY_WARNINGS_STATE_DIR → CLAUDE_CONFIG_DIR/security
+# → ~/.claude/security. See _base.state_dir for resolution precedence. Re-aliased
+# here to match the existing local name (state_dir was already a local var in
+# main() and _maybe_emit_user_notice).
+from _base import state_dir as _resolve_state_dir
+
 # Outcome codes for the sdk_bootstrap metric. Values are stable for telemetry.
 NOOP_SYSTEM = 0      # claude_agent_sdk already importable in system python
 NOOP_VENV = 1        # venv already built and SDK imports from it
@@ -90,10 +96,7 @@ def main() -> tuple[int, str, str]:
     if _sdk_on_syspath():
         return NOOP_SYSTEM, "", ""
 
-    state_dir = Path(
-        os.environ.get("SECURITY_WARNINGS_STATE_DIR")
-        or os.path.expanduser("~/.claude/security")
-    )
+    state_dir = Path(_resolve_state_dir())
     venv = state_dir / "agent-sdk-venv"
     # Windows venvs put the interpreter at Scripts\python.exe; POSIX uses bin/python.
     if sys.platform == "win32":
@@ -239,10 +242,7 @@ def _maybe_emit_user_notice(outcome: int, pv: int) -> str | None:
     if outcome != HOOK_PY_INCOMPATIBLE:
         return None
     try:
-        state_dir = Path(
-            os.environ.get("SECURITY_WARNINGS_STATE_DIR")
-            or os.path.expanduser("~/.claude/security")
-        )
+        state_dir = Path(_resolve_state_dir())
         marker = state_dir / f".agentic_unavailable_notice_v{pv or 0}"
         if marker.exists():
             return None
diff --git a/plugins/security-guidance/hooks/llm.py b/plugins/security-guidance/hooks/llm.py
index bd47aa43..5cb55f54 100644
--- a/plugins/security-guidance/hooks/llm.py
+++ b/plugins/security-guidance/hooks/llm.py
@@ -27,7 +27,7 @@ from typing import Optional, Tuple, Dict, Any, List
 
 import extensibility
 import review_api
-from _base import debug_log, _record_usage, _PV, PROVENANCE_TAG  # noqa: F401
+from _base import debug_log, _record_usage, _PV, PROVENANCE_TAG, state_dir as _resolve_state_dir  # noqa: F401
 from session_state import with_locked_state
 
 
@@ -355,10 +355,7 @@ def _call_claude_via_sdk(prompt, output_schema, *, max_tokens=16000, model=None)
         # Try the venv ensure_agent_sdk.py builds. Same fallback logic as
         # agentic_review() — duplicated here so the 3P path doesn't require
         # the agentic path to have run first.
-        _state_dir = os.environ.get(
-            "SECURITY_WARNINGS_STATE_DIR",
-            os.path.expanduser("~/.claude/security"),
-        )
+        _state_dir = _resolve_state_dir()
         _inject_agent_sdk_venv_into_syspath(_state_dir)
         try:
             import asyncio as _asyncio  # noqa: F811
@@ -1145,10 +1142,7 @@ def agentic_review(
         # ~/.claude/security/ with the SDK installed; try that as a fallback
         # before giving up. The system import is attempted first so users
         # who DO have it never touch the venv.
-        _state_dir = os.environ.get(
-            "SECURITY_WARNINGS_STATE_DIR",
-            os.path.expanduser("~/.claude/security"),
-        )
+        _state_dir = _resolve_state_dir()
         _venv_tried = _inject_agent_sdk_venv_into_syspath(_state_dir)
         try:
             import asyncio as _asyncio  # noqa: F811
diff --git a/plugins/security-guidance/hooks/security_reminder_hook.py b/plugins/security-guidance/hooks/security_reminder_hook.py
index ffc9ba3c..73a36f95 100755
--- a/plugins/security-guidance/hooks/security_reminder_hook.py
+++ b/plugins/security-guidance/hooks/security_reminder_hook.py
@@ -82,6 +82,7 @@ from _base import (  # noqa: E402,F401
     PROVENANCE_TAG, PROVENANCE_BANNER,
     _read_plugin_version_int, _PV, _USAGE, _USAGE_LOCK,
     _PRICE_PER_MTOK, _PRICE_DEFAULT, _record_usage, _usage_metrics,
+    state_dir as _resolve_state_dir,
 )
 import extensibility  # noqa: E402
 from patterns import (  # noqa: E402,F401
@@ -1971,10 +1972,7 @@ def handle_stop_hook(input_data):
     })
     sys.exit(0)
 
-_SDK_BOOTSTRAP_THROTTLE = os.path.join(
-    os.environ.get("SECURITY_WARNINGS_STATE_DIR")
-    or os.path.expanduser("~/.claude/security"),
-    ".sdk_bootstrap_spawned")
+_SDK_BOOTSTRAP_THROTTLE = os.path.join(_resolve_state_dir(), ".sdk_bootstrap_spawned")
 
 def _maybe_bootstrap_agent_sdk_async():
     """Fire-and-forget SDK bootstrap, for remote-pod environments.
diff --git a/plugins/security-guidance/hooks/session_state.py b/plugins/security-guidance/hooks/session_state.py
index 4ccd15e8..8dbadfd2 100644
--- a/plugins/security-guidance/hooks/session_state.py
+++ b/plugins/security-guidance/hooks/session_state.py
@@ -19,7 +19,7 @@ import os
 import re
 from datetime import datetime
 
-from _base import debug_log
+from _base import debug_log, state_dir as _state_dir
 
 
 def _state_key(session_id):
@@ -36,20 +36,20 @@ def _state_key(session_id):
 
 def get_state_file(session_id):
     """Get session-specific state file path."""
-    state_dir = os.environ.get("SECURITY_WARNINGS_STATE_DIR", os.path.expanduser("~/.claude/security"))
+    state_dir = _state_dir()
     return os.path.join(state_dir, f"security_warnings_state_{_state_key(session_id)}.json")
 
 
 def get_lock_file(session_id):
     """Get session-specific lock file path."""
-    state_dir = os.environ.get("SECURITY_WARNINGS_STATE_DIR", os.path.expanduser("~/.claude/security"))
+    state_dir = _state_dir()
     return os.path.join(state_dir, f"security_warnings_state_{_state_key(session_id)}.lock")
 
 
 def cleanup_old_state_files():
     """Remove state files and lock files older than 30 days."""
     try:
-        state_dir = os.environ.get("SECURITY_WARNINGS_STATE_DIR", os.path.expanduser("~/.claude/security"))
+        state_dir = _state_dir()
         if not os.path.exists(state_dir):
             return