track taint through string coercions for js/prototype-polluting-assignment

Author: erik-krogh

javascript/ql/lib/semmle/javascript/security/dataflow/PrototypePollutingAssignmentQuery.qll

@@ -31,7 +31,13 @@ class Configuration extends TaintTracking::Configuration {
     node instanceof Sanitizer
     or
     // Concatenating with a string will in practice prevent the string `__proto__` from arising.
-    node instanceof StringOps::ConcatenationRoot
+    exists(StringOps::ConcatenationRoot root | node = root |
+      // Exclude the string coercion `"" + node` from this filter.
+      not (
+        strictcount(root.getALeaf()) = 2 and
+        root.getALeaf().getStringValue() = ""
+      )
+    )
   }
 
   override predicate isAdditionalFlowStep(

javascript/ql/test/query-tests/Security/CWE-915/PrototypePollutingAssignment/PrototypePollutingAssignment.expected

@@ -56,6 +56,17 @@ nodes
 | tst.js:45:9:45:11 | obj |
 | tst.js:48:9:48:11 | obj |
 | tst.js:48:9:48:11 | obj |
+| tst.js:77:9:77:38 | taint |
+| tst.js:77:17:77:38 | String( ... y.data) |
+| tst.js:77:24:77:37 | req.query.data |
+| tst.js:77:24:77:37 | req.query.data |
+| tst.js:80:5:80:17 | object[taint] |
+| tst.js:80:5:80:17 | object[taint] |
+| tst.js:80:12:80:16 | taint |
+| tst.js:82:5:82:22 | object["" + taint] |
+| tst.js:82:5:82:22 | object["" + taint] |
+| tst.js:82:12:82:21 | "" + taint |
+| tst.js:82:17:82:21 | taint |
 edges
 | lib.js:1:38:1:40 | obj | lib.js:6:7:6:9 | obj |
 | lib.js:1:38:1:40 | obj | lib.js:6:7:6:9 | obj |
@@ -113,6 +124,16 @@ edges
 | tst.js:33:23:33:25 | obj | tst.js:45:9:45:11 | obj |
 | tst.js:33:23:33:25 | obj | tst.js:48:9:48:11 | obj |
 | tst.js:33:23:33:25 | obj | tst.js:48:9:48:11 | obj |
+| tst.js:77:9:77:38 | taint | tst.js:80:12:80:16 | taint |
+| tst.js:77:9:77:38 | taint | tst.js:82:17:82:21 | taint |
+| tst.js:77:17:77:38 | String( ... y.data) | tst.js:77:9:77:38 | taint |
+| tst.js:77:24:77:37 | req.query.data | tst.js:77:17:77:38 | String( ... y.data) |
+| tst.js:77:24:77:37 | req.query.data | tst.js:77:17:77:38 | String( ... y.data) |
+| tst.js:80:12:80:16 | taint | tst.js:80:5:80:17 | object[taint] |
+| tst.js:80:12:80:16 | taint | tst.js:80:5:80:17 | object[taint] |
+| tst.js:82:12:82:21 | "" + taint | tst.js:82:5:82:22 | object["" + taint] |
+| tst.js:82:12:82:21 | "" + taint | tst.js:82:5:82:22 | object["" + taint] |
+| tst.js:82:17:82:21 | taint | tst.js:82:12:82:21 | "" + taint |
 #select
 | lib.js:6:7:6:9 | obj | lib.js:1:43:1:46 | path | lib.js:6:7:6:9 | obj | This assignment may alter Object.prototype if a malicious '__proto__' string is injected from $@. | lib.js:1:43:1:46 | path | here |
 | lib.js:15:3:15:14 | obj[path[0]] | lib.js:14:38:14:41 | path | lib.js:15:3:15:14 | obj[path[0]] | This assignment may alter Object.prototype if a malicious '__proto__' string is injected from $@. | lib.js:14:38:14:41 | path | here |
@@ -124,3 +145,5 @@ edges
 | tst.js:39:9:39:11 | obj | tst.js:5:24:5:37 | req.query.data | tst.js:39:9:39:11 | obj | This assignment may alter Object.prototype if a malicious '__proto__' string is injected from $@. | tst.js:5:24:5:37 | req.query.data | here |
 | tst.js:45:9:45:11 | obj | tst.js:5:24:5:37 | req.query.data | tst.js:45:9:45:11 | obj | This assignment may alter Object.prototype if a malicious '__proto__' string is injected from $@. | tst.js:5:24:5:37 | req.query.data | here |
 | tst.js:48:9:48:11 | obj | tst.js:5:24:5:37 | req.query.data | tst.js:48:9:48:11 | obj | This assignment may alter Object.prototype if a malicious '__proto__' string is injected from $@. | tst.js:5:24:5:37 | req.query.data | here |
+| tst.js:80:5:80:17 | object[taint] | tst.js:77:24:77:37 | req.query.data | tst.js:80:5:80:17 | object[taint] | This assignment may alter Object.prototype if a malicious '__proto__' string is injected from $@. | tst.js:77:24:77:37 | req.query.data | here |
+| tst.js:82:5:82:22 | object["" + taint] | tst.js:77:24:77:37 | req.query.data | tst.js:82:5:82:22 | object["" + taint] | This assignment may alter Object.prototype if a malicious '__proto__' string is injected from $@. | tst.js:77:24:77:37 | req.query.data | here |

javascript/ql/test/query-tests/Security/CWE-915/PrototypePollutingAssignment/tst.js

@@ -71,3 +71,14 @@ class Box {
         this.foo = 'bar'; // OK - 'this' won't refer to Object.prototype
     }
 }
+
+
+app.get('/', (req, res) => {
+    let taint = String(req.query.data);
+
+    let object = {};
+    object[taint][taint] = taint; // NOT OK
+
+    object["" + taint]["" + taint] = taint; // NOT OK
+});
+