Bypass EDR NTDLL sigs (memory modification & freshload) working

modules/signatures/windows/bypass_edr_ntdll.py

@@ -0,0 +1,122 @@
+# Copyright (C) 2025 Kevin Ross
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+from lib.cuckoo.common.abstracts import Signature
+
+
+class Suspicious_NTDLL_DiskLoad(Signature):
+    name = "suspicious_ntdll_disk_load"
+    description = "Loads clean ntdll.dll from disk, possibly for syscall/anti-EDR"
+    severity = 3
+    categories = ["syscall", "anti-edr", "unhooking"]
+    authors = ["Kevin Ross"]
+    minimum = "1.3"
+    evented = True
+    ttps = ["T1562.001", "T1055"]  # MITRE v6,7,8
+
+    filter_apinames = set(["NtCreateFile", "NtCreateSection", "NtOpenFile", "NtProtectVirtualMemory", "NtReadFile"])
+
+    def __init__(self, *args, **kwargs):
+        Signature.__init__(self, *args, **kwargs)
+        self.ret = False
+        self.filehandle = ""
+        self.mapped = False
+
+    def on_call(self, call, process):
+        if call["api"] in ["NtCreateFile", "NtOpenFile"]:
+            filename = self.get_argument(call, "FileName")
+            if filename and filename.lower().endswith(r"\system32\ntdll.dll"):
+                filehandle = self.get_argument(call, "FileHandle")
+                self.filehandle = filehandle
+                self.mark_call()
+                self.ret = True
+
+        if call["api"] == ("NtReadFile"):
+            filehandle = self.get_argument(call, "FileHandle")
+            handlename = self.get_argument(call, "HandleName")
+            if self.filehandle and filehandle == self.filehandle and handlename and "ntdll.dll" in handlename.lower():
+                self.mark_call()
+
+        if call["api"] == ("NtCreateSection"):
+            filehandle = self.get_argument(call, "FileHandle")
+            filename = self.get_argument(call, "FileName")
+            if filehandle == self.filehandle and "ntdll.dll" in filename.lower():
+                self.mapped = True
+                self.mark_call()
+
+        if call["api"] == ("NtProtectVirtualMemory"):
+            if self.mapped:
+                modulename = self.get_argument(call, "ModuleName")
+                if modulename and modulename.lower() == "ntdll.dll":
+                    protection = self.get_argument(call, "NewAccessProtection")
+                    # 0x40 PAGE_EXECUTE_READWRITE, 0x80 PAGE_EXECUTE_WRITECOPY, 0x04 PAGE_READWRITE
+                    if protection in ["0x00000040", "0x00000080", "0x00000004"]:
+                        self.mark_call()
+
+    def on_complete(self):
+        return self.ret
+
+
+class NtdllMemoryUnhooking(Signature):
+    name = "ntdll_memory_unhooking"
+    description = "Modifies the memory protection of ntdll.dll to PAGE_READWRITE, indicative of EDR unhooking"
+    severity = 3
+    confidence = 100
+    categories = ["evasion"]
+    authors = ["Kevin Ross", "Gemini"]
+    minimum = "1.3"
+    evented = True
+    ttps = ["T1562.001", "T1055"]
+
+    filter_apinames = {"NtProtectVirtualMemory", "VirtualProtectEx", "VirtualProtect"}
+
+    def __init__(self, *args, **kwargs):
+        Signature.__init__(self, *args, **kwargs)
+        self.ret = False
+        self.unhooked_modules = set()
+
+    def on_call(self, call, process):
+        module_name = self.get_argument(call, "ModuleName")
+        if not module_name:
+            return
+
+        if "ntdll.dll" in module_name.lower():
+            protection = self.get_argument(call, "NewAccessProtection") or self.get_argument(call, "Protection")
+            if not protection:
+                return
+
+            try:
+                prot_val = int(protection, 16) if str(protection).startswith("0x") else int(protection)
+
+                # 0x04 is PAGE_READWRITE, 0x40 is PAGE_EXECUTE_READWRITE
+                if prot_val == 0x04 or prot_val == 0x40:
+                    self.unhooked_modules.add(module_name)
+                    self.mark_call()
+                    self.ret = True
+            except ValueError:
+                # Fallback: check the pretty_value translated by CAPE
+                for arg in call.get("arguments", []):
+                    if arg.get("name") in ("NewAccessProtection", "Protection"):
+                        pretty_prot = arg.get("pretty_value", "").upper()
+                        if "READWRITE" in pretty_prot:
+                            self.unhooked_modules.add(module_name)
+                            self.mark_call()
+                            self.ret = True
+                        break
+
+    def on_complete(self):
+        if self.ret:
+            self.data.append({"unhooked_module": list(self.unhooked_modules)})
+        return self.ret