add a Mutex feature

capa/features/common.py

@@ -296,6 +296,18 @@ class Filename(String):
         return False
 
 
+class Mutex(String):
+    # todo: add a way to tell whether this mutex was created or used
+    def __init__(self, value: str, description=None):
+        super().__init__(value, description)
+
+    def __eq__(self, other):
+        # Mutex instance is in a ruleset
+        if isinstance(other, Mutex):
+            return super().__eq__(other)
+        return False
+
+
 class Regex(String):
     def __init__(self, value: str, description=None):
         super().__init__(value, description=description)

capa/rules/__init__.py

@@ -265,6 +265,8 @@ def parse_feature(key: str):
         return capa.features.common.Registry
     elif key == "filename":
         return capa.features.common.Filename
+    elif key == "mutex":
+        return capa.features.common.Mutex
     elif key == "bytes":
         return capa.features.common.Bytes
     elif key == "number":