Merge pull request #9176 from geoffw0/xxe9

C++: Clean up the XXE query QL.

cpp/ql/src/Security/CWE/CWE-611/Libxml2.qll

@@ -0,0 +1,78 @@
+/**
+ * Models the libxml2 XML library.
+ */
+
+import cpp
+import XML
+import semmle.code.cpp.valuenumbering.GlobalValueNumbering
+
+/**
+ * A call to a `libxml2` function that parses XML.
+ */
+class Libxml2ParseCall extends FunctionCall {
+  int optionsArg;
+
+  Libxml2ParseCall() {
+    exists(string fname | this.getTarget().getName() = fname |
+      fname = "xmlCtxtUseOptions" and optionsArg = 1
+      or
+      fname = "xmlReadFile" and optionsArg = 2
+      or
+      fname = ["xmlCtxtReadFile", "xmlParseInNodeContext", "xmlReadDoc", "xmlReadFd"] and
+      optionsArg = 3
+      or
+      fname = ["xmlCtxtReadDoc", "xmlCtxtReadFd", "xmlReadMemory"] and optionsArg = 4
+      or
+      fname = ["xmlCtxtReadMemory", "xmlReadIO"] and optionsArg = 5
+      or
+      fname = "xmlCtxtReadIO" and optionsArg = 6
+    )
+  }
+
+  /**
+   * Gets the argument that specifies `xmlParserOption`s.
+   */
+  Expr getOptions() { result = this.getArgument(optionsArg) }
+}
+
+/**
+ * An `xmlParserOption` for `libxml2` that is considered unsafe.
+ */
+class Libxml2BadOption extends EnumConstant {
+  Libxml2BadOption() { this.getName() = ["XML_PARSE_NOENT", "XML_PARSE_DTDLOAD"] }
+}
+
+/**
+ * The libxml2 XML library.
+ */
+class LibXml2Library extends XmlLibrary {
+  LibXml2Library() { this = "LibXml2Library" }
+
+  override predicate configurationSource(DataFlow::Node node, string flowstate) {
+    // source is an `options` argument on a libxml2 parse call that specifies
+    // at least one unsafe option.
+    //
+    // note: we don't need to track an XML object for libxml2, so we don't
+    // really need data flow. Nevertheless we jam it into this configuration,
+    // with matching sources and sinks. This allows results to be presented by
+    // the same query, in a consistent way as other results with flow paths.
+    exists(Libxml2ParseCall call, Expr options |
+      options = call.getOptions() and
+      node.asExpr() = options and
+      flowstate = "libxml2" and
+      exists(Libxml2BadOption opt |
+        globalValueNumber(options).getAnExpr().getValue().toInt().bitAnd(opt.getValue().toInt()) !=
+          0
+      )
+    )
+  }
+
+  override predicate configurationSink(DataFlow::Node node, string flowstate) {
+    // sink is the `options` argument on a `libxml2` parse call.
+    exists(Libxml2ParseCall call, Expr options |
+      options = call.getOptions() and
+      node.asExpr() = options and
+      flowstate = "libxml2"
+    )
+  }
+}

cpp/ql/src/Security/CWE/CWE-611/XML.qll

@@ -0,0 +1,55 @@
+/**
+ * Provides a abstract classes for modeling XML libraries. This design is
+ * currently specialized for the purposes of the XXE query.
+ */
+
+import cpp
+import semmle.code.cpp.ir.dataflow.DataFlow
+import Xerces
+import Libxml2
+
+/**
+ * A flow state representing a possible configuration of an XML object.
+ */
+abstract class XxeFlowState extends DataFlow::FlowState {
+  bindingset[this]
+  XxeFlowState() { any() } // required characteristic predicate
+}
+
+/**
+ * An XML library or interface.
+ */
+abstract class XmlLibrary extends string {
+  bindingset[this]
+  XmlLibrary() { any() } // required characteristic predicate
+
+  /**
+   * Holds if `node` is the source node for a potentially unsafe configuration
+   * object for this XML library, along with `flowstate` representing its
+   * initial state.
+   */
+  abstract predicate configurationSource(DataFlow::Node node, string flowstate);
+
+  /**
+   * Holds if `node` is  the sink node where an unsafe configuration object is
+   * used to interpret XML.
+   */
+  abstract predicate configurationSink(DataFlow::Node node, string flowstate);
+}
+
+/**
+ * An `Expr` that changes the configuration of an XML object, transforming the
+ * `XxeFlowState` that flows through it.
+ */
+abstract class XxeFlowStateTransformer extends Expr {
+  /**
+   * Gets the flow state that `flowstate` is transformed into.
+   *
+   * Due to limitations of the implementation the transformation defined by this
+   * predicate must be idempotent, that is, for any input `x` it must be that:
+   * ```
+   * transform(transform(x)) = transform(x)
+   * ```
+   */
+  abstract XxeFlowState transform(XxeFlowState flowstate);
+}

cpp/ql/src/Security/CWE/CWE-611/XXE.ql

@@ -13,344 +13,8 @@
  */
 
 import cpp
-import semmle.code.cpp.ir.dataflow.DataFlow
+import XML
 import DataFlow::PathGraph
-import semmle.code.cpp.ir.IR
-import semmle.code.cpp.valuenumbering.GlobalValueNumbering
-
-/**
- * A flow state representing a possible configuration of an XML object.
- */
-abstract class XXEFlowState extends DataFlow::FlowState {
-  bindingset[this]
-  XXEFlowState() { any() } // required characteristic predicate
-}
-
-/**
- * An `Expr` that changes the configuration of an XML object, transforming the
- * `XXEFlowState` that flows through it.
- */
-abstract class XXEFlowStateTransformer extends Expr {
-  /**
-   * Gets the flow state that `flowstate` is transformed into.
-   *
-   * Due to limitations of the implementation the transformation defined by this
-   * predicate must be idempotent, that is, for any input `x` it must be that:
-   * ```
-   * transform(transform(x)) = transform(x)
-   * ```
-   */
-  abstract XXEFlowState transform(XXEFlowState flowstate);
-}
-
-/**
- * The `AbstractDOMParser` class.
- */
-class AbstractDOMParserClass extends Class {
-  AbstractDOMParserClass() { this.hasName("AbstractDOMParser") }
-}
-
-/**
- * The `XercesDOMParser` class.
- */
-class XercesDOMParserClass extends Class {
-  XercesDOMParserClass() { this.hasName("XercesDOMParser") }
-}
-
-/**
- * The `DOMLSParser` class.
- */
-class DomLSParserClass extends Class {
-  DomLSParserClass() { this.hasName("DOMLSParser") }
-}
-
-/**
- * The `SAXParser` class.
- */
-class SaxParserClass extends Class {
-  SaxParserClass() { this.hasName("SAXParser") }
-}
-
-/**
- * The `SAX2XMLReader` class.
- */
-class Sax2XmlReader extends Class {
-  Sax2XmlReader() { this.hasName("SAX2XMLReader") }
-}
-
-/**
- * Gets a valid flow state for `AbstractDOMParser` or `SAXParser` flow.
- *
- * These flow states take the form `Xerces-A-B`, where:
- *  - A is 1 if `setDisableDefaultEntityResolution` is `true`, 0 otherwise.
- *  - B is 1 if `setCreateEntityReferenceNodes` is `true`, 0 otherwise.
- */
-predicate encodeXercesFlowState(
-  string flowstate, int disabledDefaultEntityResolution, int createEntityReferenceNodes
-) {
-  flowstate = "Xerces-0-0" and
-  disabledDefaultEntityResolution = 0 and
-  createEntityReferenceNodes = 0
-  or
-  flowstate = "Xerces-0-1" and
-  disabledDefaultEntityResolution = 0 and
-  createEntityReferenceNodes = 1
-  or
-  flowstate = "Xerces-1-0" and
-  disabledDefaultEntityResolution = 1 and
-  createEntityReferenceNodes = 0
-  or
-  flowstate = "Xerces-1-1" and
-  disabledDefaultEntityResolution = 1 and
-  createEntityReferenceNodes = 1
-}
-
-/**
- * A flow state representing the configuration of an `AbstractDOMParser` or
- * `SAXParser` object.
- */
-class XercesFlowState extends XXEFlowState {
-  XercesFlowState() { encodeXercesFlowState(this, _, _) }
-}
-
-/**
- * A flow state transformer for a call to
- * `AbstractDOMParser.setDisableDefaultEntityResolution` or
- * `SAXParser.setDisableDefaultEntityResolution`. Transforms the flow
- * state through the qualifier according to the setting in the parameter.
- */
-class DisableDefaultEntityResolutionTransformer extends XXEFlowStateTransformer {
-  Expr newValue;
-
-  DisableDefaultEntityResolutionTransformer() {
-    exists(Call call, Function f |
-      call.getTarget() = f and
-      (
-        f.getDeclaringType() instanceof AbstractDOMParserClass or
-        f.getDeclaringType() instanceof SaxParserClass
-      ) and
-      f.hasName("setDisableDefaultEntityResolution") and
-      this = call.getQualifier() and
-      newValue = call.getArgument(0)
-    )
-  }
-
-  final override XXEFlowState transform(XXEFlowState flowstate) {
-    exists(int createEntityReferenceNodes |
-      encodeXercesFlowState(flowstate, _, createEntityReferenceNodes) and
-      (
-        globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // true
-        encodeXercesFlowState(result, 1, createEntityReferenceNodes)
-        or
-        not globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // false or unknown
-        encodeXercesFlowState(result, 0, createEntityReferenceNodes)
-      )
-    )
-  }
-}
-
-/**
- * A flow state transformer for a call to
- * `AbstractDOMParser.setCreateEntityReferenceNodes`. Transforms the flow
- * state through the qualifier according to the setting in the parameter.
- */
-class CreateEntityReferenceNodesTransformer extends XXEFlowStateTransformer {
-  Expr newValue;
-
-  CreateEntityReferenceNodesTransformer() {
-    exists(Call call, Function f |
-      call.getTarget() = f and
-      f.getClassAndName("setCreateEntityReferenceNodes") instanceof AbstractDOMParserClass and
-      this = call.getQualifier() and
-      newValue = call.getArgument(0)
-    )
-  }
-
-  final override XXEFlowState transform(XXEFlowState flowstate) {
-    exists(int disabledDefaultEntityResolution |
-      encodeXercesFlowState(flowstate, disabledDefaultEntityResolution, _) and
-      (
-        globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // true
-        encodeXercesFlowState(result, disabledDefaultEntityResolution, 1)
-        or
-        not globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // false or unknown
-        encodeXercesFlowState(result, disabledDefaultEntityResolution, 0)
-      )
-    )
-  }
-}
-
-/**
- * The `XMLUni.fgXercesDisableDefaultEntityResolution` constant.
- */
-class FeatureDisableDefaultEntityResolution extends Variable {
-  FeatureDisableDefaultEntityResolution() {
-    this.getName() = "fgXercesDisableDefaultEntityResolution" and
-    this.getDeclaringType().getName() = "XMLUni"
-  }
-}
-
-/**
- * A flow state transformer for a call to `SAX2XMLReader.setFeature`
- * specifying the feature `XMLUni::fgXercesDisableDefaultEntityResolution`.
- * Transforms the flow state through the qualifier according to this setting.
- */
-class SetFeatureTransformer extends XXEFlowStateTransformer {
-  Expr newValue;
-
-  SetFeatureTransformer() {
-    exists(Call call, Function f |
-      call.getTarget() = f and
-      f.getClassAndName("setFeature") instanceof Sax2XmlReader and
-      this = call.getQualifier() and
-      globalValueNumber(call.getArgument(0)).getAnExpr().(VariableAccess).getTarget() instanceof
-        FeatureDisableDefaultEntityResolution and
-      newValue = call.getArgument(1)
-    )
-  }
-
-  final override XXEFlowState transform(XXEFlowState flowstate) {
-    exists(int createEntityReferenceNodes |
-      encodeXercesFlowState(flowstate, _, createEntityReferenceNodes) and
-      (
-        globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // true
-        encodeXercesFlowState(result, 1, createEntityReferenceNodes)
-        or
-        not globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // false or unknown
-        encodeXercesFlowState(result, 0, createEntityReferenceNodes)
-      )
-    )
-  }
-}
-
-/**
- * The `DOMLSParser.getDomConfig` function.
- */
-class GetDomConfig extends Function {
-  GetDomConfig() { this.getClassAndName("getDomConfig") instanceof DomLSParserClass }
-}
-
-/**
- * The `DOMConfiguration.setParameter` function.
- */
-class DomConfigurationSetParameter extends Function {
-  DomConfigurationSetParameter() {
-    this.getClassAndName("setParameter").getName() = "DOMConfiguration"
-  }
-}
-
-/**
- * A flow state transformer for a call to `DOMConfiguration.setParameter`
- * specifying the feature `XMLUni::fgXercesDisableDefaultEntityResolution`.
- * This is a slightly more complex transformer because the qualifier is a
- * `DOMConfiguration` pointer returned by `DOMLSParser.getDomConfig` - and it
- * is *that* qualifier we want to transform the flow state of.
- */
-class DomConfigurationSetParameterTransformer extends XXEFlowStateTransformer {
-  Expr newValue;
-
-  DomConfigurationSetParameterTransformer() {
-    exists(FunctionCall getDomConfigCall, FunctionCall setParameterCall |
-      // this is the qualifier of a call to `DOMLSParser.getDomConfig`.
-      getDomConfigCall.getTarget() instanceof GetDomConfig and
-      this = getDomConfigCall.getQualifier() and
-      // `setParameterCall` is a call to `setParameter` on the return value of
-      // the same call to `DOMLSParser.getDomConfig`.
-      setParameterCall.getTarget() instanceof DomConfigurationSetParameter and
-      globalValueNumber(setParameterCall.getQualifier()).getAnExpr() = getDomConfigCall and
-      // the parameter being set is
-      // `XMLUni::fgXercesDisableDefaultEntityResolution`.
-      globalValueNumber(setParameterCall.getArgument(0)).getAnExpr().(VariableAccess).getTarget()
-        instanceof FeatureDisableDefaultEntityResolution and
-      // the value being set is `newValue`.
-      newValue = setParameterCall.getArgument(1)
-    )
-  }
-
-  final override XXEFlowState transform(XXEFlowState flowstate) {
-    exists(int createEntityReferenceNodes |
-      encodeXercesFlowState(flowstate, _, createEntityReferenceNodes) and
-      (
-        globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // true
-        encodeXercesFlowState(result, 1, createEntityReferenceNodes)
-        or
-        not globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // false or unknown
-        encodeXercesFlowState(result, 0, createEntityReferenceNodes)
-      )
-    )
-  }
-}
-
-/**
- * The `AbstractDOMParser.parse`, `DOMLSParserClass.parse`, `SAXParser.parse`
- * or `SAX2XMLReader.parse` method.
- */
-class ParseFunction extends Function {
-  ParseFunction() {
-    this.getClassAndName("parse") instanceof AbstractDOMParserClass or
-    this.getClassAndName("parse") instanceof DomLSParserClass or
-    this.getClassAndName("parse") instanceof SaxParserClass or
-    this.getClassAndName("parse") instanceof Sax2XmlReader
-  }
-}
-
-/**
- * The `createLSParser` function that returns a newly created `DOMLSParser`
- * object.
- */
-class CreateLSParser extends Function {
-  CreateLSParser() {
-    this.hasName("createLSParser") and
-    this.getUnspecifiedType().(PointerType).getBaseType() instanceof DomLSParserClass // returns a `DOMLSParser *`.
-  }
-}
-
-/**
- * The `createXMLReader` function that returns a newly created `SAX2XMLReader`
- * object.
- */
-class CreateXmlReader extends Function {
-  CreateXmlReader() {
-    this.hasName("createXMLReader") and
-    this.getUnspecifiedType().(PointerType).getBaseType() instanceof Sax2XmlReader // returns a `SAX2XMLReader *`.
-  }
-}
-
-/**
- * A call to a `libxml2` function that parses XML.
- */
-class Libxml2ParseCall extends FunctionCall {
-  int optionsArg;
-
-  Libxml2ParseCall() {
-    exists(string fname | this.getTarget().getName() = fname |
-      fname = "xmlCtxtUseOptions" and optionsArg = 1
-      or
-      fname = "xmlReadFile" and optionsArg = 2
-      or
-      fname = ["xmlCtxtReadFile", "xmlParseInNodeContext", "xmlReadDoc", "xmlReadFd"] and
-      optionsArg = 3
-      or
-      fname = ["xmlCtxtReadDoc", "xmlCtxtReadFd", "xmlReadMemory"] and optionsArg = 4
-      or
-      fname = ["xmlCtxtReadMemory", "xmlReadIO"] and optionsArg = 5
-      or
-      fname = "xmlCtxtReadIO" and optionsArg = 6
-    )
-  }
-
-  /**
-   * Gets the argument that specifies `xmlParserOption`s.
-   */
-  Expr getOptions() { result = this.getArgument(optionsArg) }
-}
-
-/**
- * An `xmlParserOption` for `libxml2` that is considered unsafe.
- */
-class Libxml2BadOption extends EnumConstant {
-  Libxml2BadOption() { this.getName() = ["XML_PARSE_NOENT", "XML_PARSE_DTDLOAD"] }
-}
 
 /**
  * A configuration for tracking XML objects and their states.
@@ -359,85 +23,25 @@ class XXEConfiguration extends DataFlow::Configuration {
   XXEConfiguration() { this = "XXEConfiguration" }
 
   override predicate isSource(DataFlow::Node node, string flowstate) {
-    // source is the write on `this` of a call to the `XercesDOMParser`
-    // constructor.
-    exists(CallInstruction call |
-      call.getStaticCallTarget() = any(XercesDOMParserClass c).getAConstructor() and
-      node.asInstruction().(WriteSideEffectInstruction).getDestinationAddress() =
-        call.getThisArgument() and
-      encodeXercesFlowState(flowstate, 0, 1) // default configuration
-    )
-    or
-    // source is the result of a call to `createLSParser`.
-    exists(Call call |
-      call.getTarget() instanceof CreateLSParser and
-      call = node.asExpr() and
-      encodeXercesFlowState(flowstate, 0, 1) // default configuration
-    )
-    or
-    // source is the write on `this` of a call to the `SAXParser`
-    // constructor.
-    exists(CallInstruction call |
-      call.getStaticCallTarget() = any(SaxParserClass c).getAConstructor() and
-      node.asInstruction().(WriteSideEffectInstruction).getDestinationAddress() =
-        call.getThisArgument() and
-      encodeXercesFlowState(flowstate, 0, 1) // default configuration
-    )
-    or
-    // source is the result of a call to `createXMLReader`.
-    exists(Call call |
-      call.getTarget() instanceof CreateXmlReader and
-      call = node.asExpr() and
-      encodeXercesFlowState(flowstate, 0, 1) // default configuration
-    )
-    or
-    // source is an `options` argument on a `libxml2` parse call that specifies
-    // at least one unsafe option.
-    //
-    // note: we don't need to track an XML object for `libxml2`, so we don't
-    // really need data flow. Nevertheless we jam it into this configuration,
-    // with matching sources and sinks. This allows results to be presented by
-    // the same query, in a consistent way as other results with flow paths.
-    exists(Libxml2ParseCall call, Expr options |
-      options = call.getOptions() and
-      node.asExpr() = options and
-      flowstate = "libxml2" and
-      exists(Libxml2BadOption opt |
-        globalValueNumber(options).getAnExpr().getValue().toInt().bitAnd(opt.getValue().toInt()) !=
-          0
-      )
-    )
+    any(XmlLibrary l).configurationSource(node, flowstate)
   }
 
   override predicate isSink(DataFlow::Node node, string flowstate) {
-    // sink is the read of the qualifier of a call to `parse`.
-    exists(Call call |
-      call.getTarget() instanceof ParseFunction and
-      call.getQualifier() = node.asConvertedExpr()
-    ) and
-    flowstate instanceof XercesFlowState and
-    not encodeXercesFlowState(flowstate, 1, 1) // safe configuration
-    or
-    // sink is the `options` argument on a `libxml2` parse call.
-    exists(Libxml2ParseCall call, Expr options |
-      options = call.getOptions() and
-      node.asExpr() = options and
-      flowstate = "libxml2"
-    )
+    any(XmlLibrary l).configurationSink(node, flowstate)
   }
 
   override predicate isAdditionalFlowStep(
     DataFlow::Node node1, string state1, DataFlow::Node node2, string state2
   ) {
-    // create additional flow steps for `XXEFlowStateTransformer`s
-    state2 = node2.asConvertedExpr().(XXEFlowStateTransformer).transform(state1) and
+    // create additional flow steps for `XxeFlowStateTransformer`s
+    state2 = node2.asConvertedExpr().(XxeFlowStateTransformer).transform(state1) and
     DataFlow::simpleLocalFlowStep(node1, node2)
   }
 
   override predicate isBarrier(DataFlow::Node node, string flowstate) {
     // when the flowstate is transformed at a call node, block the original
     // flowstate value.
-    node.asConvertedExpr().(XXEFlowStateTransformer).transform(flowstate) != flowstate
+    node.asConvertedExpr().(XxeFlowStateTransformer).transform(flowstate) != flowstate
   }
 }
 

cpp/ql/src/Security/CWE/CWE-611/Xerces.qll

@@ -0,0 +1,376 @@
+/**
+ * Models the Xerces XML library.
+ */
+
+import cpp
+import XML
+import semmle.code.cpp.valuenumbering.GlobalValueNumbering
+import semmle.code.cpp.ir.IR
+
+/**
+ * Gets a valid flow state for `AbstractDOMParser` or `SAXParser` flow.
+ *
+ * These flow states take the form `Xerces-A-B`, where:
+ *  - A is 1 if `setDisableDefaultEntityResolution` is `true`, 0 otherwise.
+ *  - B is 1 if `setCreateEntityReferenceNodes` is `true`, 0 otherwise.
+ */
+predicate encodeXercesFlowState(
+  string flowstate, int disabledDefaultEntityResolution, int createEntityReferenceNodes
+) {
+  flowstate = "Xerces-0-0" and
+  disabledDefaultEntityResolution = 0 and
+  createEntityReferenceNodes = 0
+  or
+  flowstate = "Xerces-0-1" and
+  disabledDefaultEntityResolution = 0 and
+  createEntityReferenceNodes = 1
+  or
+  flowstate = "Xerces-1-0" and
+  disabledDefaultEntityResolution = 1 and
+  createEntityReferenceNodes = 0
+  or
+  flowstate = "Xerces-1-1" and
+  disabledDefaultEntityResolution = 1 and
+  createEntityReferenceNodes = 1
+}
+
+/**
+ * A flow state representing the configuration of an `AbstractDOMParser` or
+ * `SAXParser` object.
+ */
+class XercesFlowState extends XxeFlowState {
+  XercesFlowState() { encodeXercesFlowState(this, _, _) }
+}
+
+/**
+ * The `AbstractDOMParser` class.
+ */
+class AbstractDomParserClass extends Class {
+  AbstractDomParserClass() { this.hasName("AbstractDOMParser") }
+}
+
+/**
+ * The `XercesDOMParser` class.
+ */
+class XercesDomParserClass extends Class {
+  XercesDomParserClass() { this.hasName("XercesDOMParser") }
+}
+
+/**
+ * The `XercesDOMParser` interface for the Xerces XML library.
+ */
+class XercesDomParserLibrary extends XmlLibrary {
+  XercesDomParserLibrary() { this = "XercesDomParserLibrary" }
+
+  override predicate configurationSource(DataFlow::Node node, string flowstate) {
+    // source is the write on `this` of a call to the `XercesDOMParser`
+    // constructor.
+    exists(CallInstruction call |
+      call.getStaticCallTarget() = any(XercesDomParserClass c).getAConstructor() and
+      node.asInstruction().(WriteSideEffectInstruction).getDestinationAddress() =
+        call.getThisArgument() and
+      encodeXercesFlowState(flowstate, 0, 1) // default configuration
+    )
+  }
+
+  override predicate configurationSink(DataFlow::Node node, string flowstate) {
+    // sink is the read of the qualifier of a call to `AbstractDOMParser.parse`.
+    exists(Call call |
+      call.getTarget().getClassAndName("parse") instanceof AbstractDomParserClass and
+      call.getQualifier() = node.asConvertedExpr()
+    ) and
+    flowstate instanceof XercesFlowState and
+    not encodeXercesFlowState(flowstate, 1, 1) // safe configuration
+  }
+}
+
+/**
+ * The `DOMLSParser` class.
+ */
+class DomLSParserClass extends Class {
+  DomLSParserClass() { this.hasName("DOMLSParser") }
+}
+
+/**
+ * The `createLSParser` function that returns a newly created `DOMLSParser`
+ * object.
+ */
+class CreateLSParser extends Function {
+  CreateLSParser() {
+    this.hasName("createLSParser") and
+    this.getUnspecifiedType().(PointerType).getBaseType() instanceof DomLSParserClass // returns a `DOMLSParser *`.
+  }
+}
+
+/**
+ * The createLSParser interface for the Xerces XML library.
+ */
+class CreateLSParserLibrary extends XmlLibrary {
+  CreateLSParserLibrary() { this = "CreateLSParserLibrary" }
+
+  override predicate configurationSource(DataFlow::Node node, string flowstate) {
+    // source is the result of a call to `createLSParser`.
+    exists(Call call |
+      call.getTarget() instanceof CreateLSParser and
+      call = node.asExpr() and
+      encodeXercesFlowState(flowstate, 0, 1) // default configuration
+    )
+  }
+
+  override predicate configurationSink(DataFlow::Node node, string flowstate) {
+    // sink is the read of the qualifier of a call to `DOMLSParserClass.parse`.
+    exists(Call call |
+      call.getTarget().getClassAndName("parse") instanceof DomLSParserClass and
+      call.getQualifier() = node.asConvertedExpr()
+    ) and
+    flowstate instanceof XercesFlowState and
+    not encodeXercesFlowState(flowstate, 1, 1) // safe configuration
+  }
+}
+
+/**
+ * The `SAXParser` class.
+ */
+class SaxParserClass extends Class {
+  SaxParserClass() { this.hasName("SAXParser") }
+}
+
+/**
+ * The `SAX2XMLReader` class.
+ */
+class Sax2XmlReader extends Class {
+  Sax2XmlReader() { this.hasName("SAX2XMLReader") }
+}
+
+/**
+ * The SAXParser interface for the Xerces XML library.
+ */
+class SaxParserLibrary extends XmlLibrary {
+  SaxParserLibrary() { this = "SaxParserLibrary" }
+
+  override predicate configurationSource(DataFlow::Node node, string flowstate) {
+    // source is the write on `this` of a call to the `SAXParser`
+    // constructor.
+    exists(CallInstruction call |
+      call.getStaticCallTarget() = any(SaxParserClass c).getAConstructor() and
+      node.asInstruction().(WriteSideEffectInstruction).getDestinationAddress() =
+        call.getThisArgument() and
+      encodeXercesFlowState(flowstate, 0, 1) // default configuration
+    )
+  }
+
+  override predicate configurationSink(DataFlow::Node node, string flowstate) {
+    // sink is the read of the qualifier of a call to `SAXParser.parse`.
+    exists(Call call |
+      call.getTarget().getClassAndName("parse") instanceof SaxParserClass and
+      call.getQualifier() = node.asConvertedExpr()
+    ) and
+    flowstate instanceof XercesFlowState and
+    not encodeXercesFlowState(flowstate, 1, 1) // safe configuration
+  }
+}
+
+/**
+ * The `createXMLReader` function that returns a newly created `SAX2XMLReader`
+ * object.
+ */
+class CreateXmlReader extends Function {
+  CreateXmlReader() {
+    this.hasName("createXMLReader") and
+    this.getUnspecifiedType().(PointerType).getBaseType() instanceof Sax2XmlReader // returns a `SAX2XMLReader *`.
+  }
+}
+
+/**
+ * The SAX2XMLReader interface for the Xerces XML library.
+ */
+class Sax2XmlReaderLibrary extends XmlLibrary {
+  Sax2XmlReaderLibrary() { this = "Sax2XmlReaderLibrary" }
+
+  override predicate configurationSource(DataFlow::Node node, string flowstate) {
+    // source is the result of a call to `createXMLReader`.
+    exists(Call call |
+      call.getTarget() instanceof CreateXmlReader and
+      call = node.asExpr() and
+      encodeXercesFlowState(flowstate, 0, 1) // default configuration
+    )
+  }
+
+  override predicate configurationSink(DataFlow::Node node, string flowstate) {
+    // sink is the read of the qualifier of a call to `SAX2XMLReader.parse`.
+    exists(Call call |
+      call.getTarget().getClassAndName("parse") instanceof Sax2XmlReader and
+      call.getQualifier() = node.asConvertedExpr()
+    ) and
+    flowstate instanceof XercesFlowState and
+    not encodeXercesFlowState(flowstate, 1, 1) // safe configuration
+  }
+}
+
+/**
+ * A flow state transformer for a call to
+ * `AbstractDOMParser.setDisableDefaultEntityResolution` or
+ * `SAXParser.setDisableDefaultEntityResolution`. Transforms the flow
+ * state through the qualifier according to the setting in the parameter.
+ */
+class DisableDefaultEntityResolutionTransformer extends XxeFlowStateTransformer {
+  Expr newValue;
+
+  DisableDefaultEntityResolutionTransformer() {
+    exists(Call call, Function f |
+      call.getTarget() = f and
+      (
+        f.getDeclaringType() instanceof AbstractDomParserClass or
+        f.getDeclaringType() instanceof SaxParserClass
+      ) and
+      f.hasName("setDisableDefaultEntityResolution") and
+      this = call.getQualifier() and
+      newValue = call.getArgument(0)
+    )
+  }
+
+  final override XxeFlowState transform(XxeFlowState flowstate) {
+    exists(int createEntityReferenceNodes |
+      encodeXercesFlowState(flowstate, _, createEntityReferenceNodes) and
+      (
+        globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // true
+        encodeXercesFlowState(result, 1, createEntityReferenceNodes)
+        or
+        not globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // false or unknown
+        encodeXercesFlowState(result, 0, createEntityReferenceNodes)
+      )
+    )
+  }
+}
+
+/**
+ * A flow state transformer for a call to
+ * `AbstractDOMParser.setCreateEntityReferenceNodes`. Transforms the flow
+ * state through the qualifier according to the setting in the parameter.
+ */
+class CreateEntityReferenceNodesTransformer extends XxeFlowStateTransformer {
+  Expr newValue;
+
+  CreateEntityReferenceNodesTransformer() {
+    exists(Call call, Function f |
+      call.getTarget() = f and
+      f.getClassAndName("setCreateEntityReferenceNodes") instanceof AbstractDomParserClass and
+      this = call.getQualifier() and
+      newValue = call.getArgument(0)
+    )
+  }
+
+  final override XxeFlowState transform(XxeFlowState flowstate) {
+    exists(int disabledDefaultEntityResolution |
+      encodeXercesFlowState(flowstate, disabledDefaultEntityResolution, _) and
+      (
+        globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // true
+        encodeXercesFlowState(result, disabledDefaultEntityResolution, 1)
+        or
+        not globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // false or unknown
+        encodeXercesFlowState(result, disabledDefaultEntityResolution, 0)
+      )
+    )
+  }
+}
+
+/**
+ * The `XMLUni.fgXercesDisableDefaultEntityResolution` constant.
+ */
+class FeatureDisableDefaultEntityResolution extends Variable {
+  FeatureDisableDefaultEntityResolution() {
+    this.getName() = "fgXercesDisableDefaultEntityResolution" and
+    this.getDeclaringType().getName() = "XMLUni"
+  }
+}
+
+/**
+ * A flow state transformer for a call to `SAX2XMLReader.setFeature`
+ * specifying the feature `XMLUni::fgXercesDisableDefaultEntityResolution`.
+ * Transforms the flow state through the qualifier according to this setting.
+ */
+class SetFeatureTransformer extends XxeFlowStateTransformer {
+  Expr newValue;
+
+  SetFeatureTransformer() {
+    exists(Call call, Function f |
+      call.getTarget() = f and
+      f.getClassAndName("setFeature") instanceof Sax2XmlReader and
+      this = call.getQualifier() and
+      globalValueNumber(call.getArgument(0)).getAnExpr().(VariableAccess).getTarget() instanceof
+        FeatureDisableDefaultEntityResolution and
+      newValue = call.getArgument(1)
+    )
+  }
+
+  final override XxeFlowState transform(XxeFlowState flowstate) {
+    exists(int createEntityReferenceNodes |
+      encodeXercesFlowState(flowstate, _, createEntityReferenceNodes) and
+      (
+        globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // true
+        encodeXercesFlowState(result, 1, createEntityReferenceNodes)
+        or
+        not globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // false or unknown
+        encodeXercesFlowState(result, 0, createEntityReferenceNodes)
+      )
+    )
+  }
+}
+
+/**
+ * The `DOMLSParser.getDomConfig` function.
+ */
+class GetDomConfig extends Function {
+  GetDomConfig() { this.getClassAndName("getDomConfig") instanceof DomLSParserClass }
+}
+
+/**
+ * The `DOMConfiguration.setParameter` function.
+ */
+class DomConfigurationSetParameter extends Function {
+  DomConfigurationSetParameter() {
+    this.getClassAndName("setParameter").getName() = "DOMConfiguration"
+  }
+}
+
+/**
+ * A flow state transformer for a call to `DOMConfiguration.setParameter`
+ * specifying the feature `XMLUni::fgXercesDisableDefaultEntityResolution`.
+ * This is a slightly more complex transformer because the qualifier is a
+ * `DOMConfiguration` pointer returned by `DOMLSParser.getDomConfig` - and it
+ * is *that* qualifier we want to transform the flow state of.
+ */
+class DomConfigurationSetParameterTransformer extends XxeFlowStateTransformer {
+  Expr newValue;
+
+  DomConfigurationSetParameterTransformer() {
+    exists(FunctionCall getDomConfigCall, FunctionCall setParameterCall |
+      // this is the qualifier of a call to `DOMLSParser.getDomConfig`.
+      getDomConfigCall.getTarget() instanceof GetDomConfig and
+      this = getDomConfigCall.getQualifier() and
+      // `setParameterCall` is a call to `setParameter` on the return value of
+      // the same call to `DOMLSParser.getDomConfig`.
+      setParameterCall.getTarget() instanceof DomConfigurationSetParameter and
+      globalValueNumber(setParameterCall.getQualifier()).getAnExpr() = getDomConfigCall and
+      // the parameter being set is
+      // `XMLUni::fgXercesDisableDefaultEntityResolution`.
+      globalValueNumber(setParameterCall.getArgument(0)).getAnExpr().(VariableAccess).getTarget()
+        instanceof FeatureDisableDefaultEntityResolution and
+      // the value being set is `newValue`.
+      newValue = setParameterCall.getArgument(1)
+    )
+  }
+
+  final override XxeFlowState transform(XxeFlowState flowstate) {
+    exists(int createEntityReferenceNodes |
+      encodeXercesFlowState(flowstate, _, createEntityReferenceNodes) and
+      (
+        globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // true
+        encodeXercesFlowState(result, 1, createEntityReferenceNodes)
+        or
+        not globalValueNumber(newValue).getAnExpr().getValue().toInt() = 1 and // false or unknown
+        encodeXercesFlowState(result, 0, createEntityReferenceNodes)
+      )
+    )
+  }
+}