Add PEP249 connection tracking through class attribute wrappers

Introduce two new Connection::InstanceSource subclasses in PEP249.qll:

- ConnectionGetterAttributeRead: recognises self._conn reads inside
  getter methods of classes whose __init__ stores a connect() call in
  that attribute. The AttrRead node coincides with the return node, so
  the existing TypeTracker returnStep propagates the connection type to
  all call sites automatically.

- ConnectionConstructorAttributeRead: recognises ClassName()._conn
  direct attribute reads on constructor-call results.

Both classes share the classStoresConnectionInInit helper predicate
that checks for the self.attr = dbapi.connect() store pattern in __init__.

Also adds test cases for the new patterns in the hdbcli test suite
and a change note.

python/ql/lib/semmle/python/frameworks/PEP249.qll

@@ -8,6 +8,7 @@ private import semmle.python.dataflow.new.DataFlow
 private import semmle.python.dataflow.new.RemoteFlowSources
 private import semmle.python.Concepts
 private import semmle.python.ApiGraphs
+private import semmle.python.dataflow.new.internal.DataFlowDispatch as DataFlowDispatch
 
 /**
  * Provides classes modeling database interfaces following PEP 249.
@@ -212,6 +213,74 @@ module PEP249 {
       ConnectCall() { this.getFunction() = connect() }
     }
 
+    /**
+     * Holds if class `cls` stores a PEP 249 database connection to `self.<attrName>`
+     * in its `__init__` method, via a direct call to a `connect` function.
+     */
+    private predicate classStoresConnectionInInit(Class cls, string attrName) {
+      exists(Function init, DataFlow::AttrWrite store |
+        cls.getAMethod() = init and
+        init.getName() = "__init__" and
+        store.getAttributeName() = attrName and
+        store.getObject().asCfgNode().getNode().(Name).getVariable() =
+          init.getArg(0).asName().getVariable() and
+        store.getValue() instanceof ConnectCall
+      )
+    }
+
+    /**
+     * A read of a connection-holding attribute within a method of a class whose
+     * `__init__` stores a PEP 249 connection in that attribute.
+     *
+     * This recognises patterns such as:
+     * ```python
+     * class Wrapper:
+     *     def __init__(self):
+     *         self._conn = dbapi.connect(...)
+     *     def get_connection(self):
+     *         return self._conn  # <-- recognised as a connection source
+     * ```
+     * Because the `AttrRead` node for `self._conn` inside `get_connection` is
+     * also the `ExtractedReturnNode` for that statement, the existing TypeTracker
+     * `returnStep` automatically propagates the connection type to all call sites
+     * of `get_connection`.
+     */
+    private class ConnectionGetterAttributeRead extends InstanceSource, DataFlow::AttrRead {
+      ConnectionGetterAttributeRead() {
+        exists(Class cls, Function method, string attrName |
+          classStoresConnectionInInit(cls, attrName) and
+          cls.getAMethod() = method and
+          method.getName() != "__init__" and
+          this.getAttributeName() = attrName and
+          this.getObject().asCfgNode().getNode().(Name).getVariable() =
+            method.getArg(0).asName().getVariable()
+        )
+      }
+    }
+
+    /**
+     * An attribute access on a constructor-call result that directly reads the
+     * connection-holding attribute.
+     *
+     * This recognises patterns such as:
+     * ```python
+     * class Wrapper:
+     *     def __init__(self):
+     *         self._conn = dbapi.connect(...)
+     *
+     * conn = Wrapper()._conn  # <-- recognised as a connection source
+     * ```
+     */
+    private class ConnectionConstructorAttributeRead extends InstanceSource, DataFlow::AttrRead {
+      ConnectionConstructorAttributeRead() {
+        exists(Class cls, string attrName |
+          classStoresConnectionInInit(cls, attrName) and
+          this.getAttributeName() = attrName and
+          DataFlowDispatch::resolveClassCall(this.getObject().asCfgNode().(CallNode), cls)
+        )
+      }
+    }
+
     /** Gets a reference to a database connection (following PEP 249). */
     private DataFlow::TypeTrackingNode instance(DataFlow::TypeTracker t) {
       t.start() and

python/ql/src/change-notes/2026-05-21-pep249-class-wrapper-connections.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Improved detection of SQL injection and other PEP 249 database-related vulnerabilities when a database connection is stored in a class instance attribute and accessed through a getter method or direct attribute read. For example, patterns like `self._conn = dbapi.connect(...)` in `__init__` followed by `return self._conn` in a getter method, or `MyClass()._conn`, are now correctly recognised as PEP 249 connection sources.

python/ql/test/library-tests/frameworks/hdbcli/pep249.py

@@ -7,3 +7,49 @@ cursor.execute("some sql", (42,))  # $ getSql="some sql"
 cursor.executemany("some sql", (42,))  # $ getSql="some sql"
     
 cursor.close()
+
+
+# ---------------------------------------------------------------------------
+# Connection stored in a class attribute and accessed via various patterns
+# ---------------------------------------------------------------------------
+
+
+class WrapperA:
+    def __init__(self):
+        self._conn = dbapi.connect(address="hostname", port=300, user="username", pass_arg="testpass")
+
+    def get_connection(self):
+        return self._conn
+
+
+# Getter called on a fresh constructor result
+conn_a1 = WrapperA().get_connection()
+cursor_a1 = conn_a1.cursor()
+cursor_a1.execute("some sql", (42,))  # $ getSql="some sql"
+
+# Getter called via a stored wrapper instance
+wrapper_instance = WrapperA()
+conn_a2 = wrapper_instance.get_connection()
+cursor_a2 = conn_a2.cursor()
+cursor_a2.execute("some sql", (42,))  # $ getSql="some sql"
+
+# Direct attribute access on a fresh constructor result
+conn_b = WrapperA()._conn
+cursor_b = conn_b.cursor()
+cursor_b.execute("some sql", (42,))  # $ getSql="some sql"
+
+
+class WrapperB:
+    """Stores the connection under a different attribute name."""
+
+    def __init__(self):
+        self._hana = dbapi.connect(address="hostname", port=300, user="username", pass_arg="testpass")
+
+    def cursor(self):
+        return self._hana.cursor()
+
+
+# Direct attribute access on a stored instance (mirrors hdb_con3 in the issue)
+conn_c = WrapperB()._hana
+cursor_c = conn_c.cursor()
+cursor_c.execute("some sql", (42,))  # $ getSql="some sql"