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Ruby : XPath Injection Query (CWE-643)
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‎ruby/ql/lib/codeql/ruby/Concepts.qll‎

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@@ -840,6 +840,58 @@ module XmlParserCall {
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}
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}
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/**
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* A data-flow node that constructs an XPath expression.
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*
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* If it is important that the XPath expression is indeed executed, then use `XPathExecution`.
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*
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* Extend this class to refine existing API models. If you want to model new APIs,
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* extend `XPathConstruction::Range` instead.
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*/
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class XPathConstruction extends DataFlow::Node instanceof XPathConstruction::Range {
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/** Gets the argument that specifies the XPath expressions to be constructed. */
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DataFlow::Node getXPath() { result = super.getXPath() }
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}
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/** Provides a class for modeling new XPath construction APIs. */
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module XPathConstruction {
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/**
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* A data-flow node that constructs an XPath expression.
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*
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* Extend this class to model new APIs. If you want to refine existing API models,
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* extend `XPathConstruction` instead.
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*/
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abstract class Range extends DataFlow::Node {
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/** Gets the argument that specifies the XPath expressions to be constructed. */
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abstract DataFlow::Node getXPath();
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}
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}
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/**
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* A data-flow node that executes an XPath expression.
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*
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* Extend this class to refine existing API models. If you want to model new APIs,
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* extend `XPathExecution::Range` instead.
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*/
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class XPathExecution extends DataFlow::Node instanceof XPathExecution::Range {
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/** Gets the argument that specifies the XPath expressions to be executed. */
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DataFlow::Node getXPath() { result = super.getXPath() }
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}
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/** Provides a class for modeling new XPath execution APIs. */
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module XPathExecution {
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/**
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* A data-flow node that executes an XPath expression.
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*
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* Extend this class to model new APIs. If you want to refine existing API models,
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* extend `XPathExecution` instead.
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*/
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abstract class Range extends DataFlow::Node {
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/** Gets the argument that specifies the XPath expressions to be executed. */
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abstract DataFlow::Node getXPath();
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}
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}
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/**
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* A data-flow node that may represent a database object in an ORM system.
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*

‎ruby/ql/lib/codeql/ruby/Frameworks.qll‎

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@@ -32,3 +32,6 @@ private import codeql.ruby.frameworks.Slim
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private import codeql.ruby.frameworks.Sinatra
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private import codeql.ruby.frameworks.Twirp
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private import codeql.ruby.frameworks.Sqlite3
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private import codeql.ruby.frameworks.Rexml
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private import codeql.ruby.frameworks.Nokogiri
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private import codeql.ruby.frameworks.Libxml

‎ruby/ql/lib/codeql/ruby/frameworks/Libxml.qll‎

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/**
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* Provides modeling for `libxml`, an XML library for Ruby.
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*/
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private import codeql.ruby.ApiGraphs
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private import codeql.ruby.dataflow.FlowSummary
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private import codeql.ruby.Concepts
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/**
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* Provides modeling for `libxml`, an XML library for Ruby.
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*/
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module Libxml {
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/**
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* Flow summary for `libxml`. Wraps a string, parsing it as an XML document.
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*/
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private class XMLSummary extends SummarizedCallable {
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XMLSummary() { this = "LibXML::XML" }
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override MethodCall getACall() { result = any(LibXmlRubyXmlParserCall c).asExpr().getExpr() }
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override predicate propagatesFlowExt(string input, string output, boolean preservesValue) {
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input = "Argument[0]" and output = "ReturnValue" and preservesValue = false
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}
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}
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/** A call that parses XML. */
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private class LibXmlRubyXmlParserCall extends DataFlow::CallNode {
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LibXmlRubyXmlParserCall() {
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this =
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[API::getTopLevelMember("LibXML").getMember("XML"), API::getTopLevelMember("XML")]
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.getMember(["Document", "Parser"])
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.getAMethodCall(["file", "io", "string"])
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}
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DataFlow::Node getInput() { result = this.getArgument(0) }
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}
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/** Execution of a XPath statement. */
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private class LibXmlXPathExecution extends XPathExecution::Range, DataFlow::CallNode {
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LibXmlXPathExecution() {
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exists(LibXmlRubyXmlParserCall parserCall |
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this = parserCall.getAMethodCall(["find", "find_first"])
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)
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}
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override DataFlow::Node getXPath() { result = this.getArgument(0) }
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}
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}

‎ruby/ql/lib/codeql/ruby/frameworks/Nokogiri.qll‎

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/**
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* Provides modeling for `nokogiri`, an XML library for Ruby.
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*/
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private import codeql.ruby.ApiGraphs
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private import codeql.ruby.dataflow.FlowSummary
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private import codeql.ruby.Concepts
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/**
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* Provides modeling for `nokogiri`, an XML library for Ruby.
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*/
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module Nokogiri {
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/**
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* Flow summary for `nokogiri`. Wraps a string, parsing it as an XML document.
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*/
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private class XMLSummary extends SummarizedCallable {
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XMLSummary() { this = "Nokogiri::XML.parse" }
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override MethodCall getACall() { result = any(NokogiriXmlParserCall p).asExpr().getExpr() }
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override predicate propagatesFlowExt(string input, string output, boolean preservesValue) {
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input = "Argument[0]" and output = "ReturnValue" and preservesValue = false
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}
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}
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/** A call that parses XML. */
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private class NokogiriXmlParserCall extends DataFlow::CallNode {
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NokogiriXmlParserCall() {
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this =
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[
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API::getTopLevelMember("Nokogiri").getMember("XML"),
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API::getTopLevelMember("Nokogiri").getMember("XML").getMember("Document"),
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API::getTopLevelMember("Nokogiri")
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.getMember("XML")
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.getMember("SAX")
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.getMember("Parser")
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.getInstance()
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].getAMethodCall("parse")
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}
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DataFlow::Node getInput() { result = this.getArgument(0) }
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}
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/** Execution of a XPath statement. */
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private class NokogiriXPathExecution extends XPathExecution::Range, DataFlow::CallNode {
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NokogiriXPathExecution() {
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exists(NokogiriXmlParserCall parserCall |
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this = parserCall.getAMethodCall(["xpath", "at_xpath", "search", "at"])
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)
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}
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override DataFlow::Node getXPath() { result = this.getArgument(0) }
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}
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}

‎ruby/ql/lib/codeql/ruby/frameworks/Rexml.qll‎

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/**
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* Provides modeling for `rexml`, an XML toolkit for Ruby.
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*/
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private import codeql.ruby.ApiGraphs
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private import codeql.ruby.dataflow.FlowSummary
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private import codeql.ruby.Concepts
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/**
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* Provides modeling for `rexml`, an XML toolkit for Ruby.
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*/
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module Rexml {
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/**
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* Flow summary for `REXML::Document.new()`. This method wraps a string, parsing it as an XML document.
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*/
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private class XMLSummary extends SummarizedCallable {
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XMLSummary() { this = "REXML::Document.new()" }
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override MethodCall getACall() { result = any(RexmlParserCall c).asExpr().getExpr() }
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override predicate propagatesFlowExt(string input, string output, boolean preservesValue) {
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input = "Argument[0]" and output = "ReturnValue" and preservesValue = false
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}
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}
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/** A call to `REXML::Document.new`, considered as a XML parsing. */
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private class RexmlParserCall extends XmlParserCall::Range, DataFlow::CallNode {
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RexmlParserCall() {
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this = API::getTopLevelMember("REXML").getMember("Document").getAnInstantiation()
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}
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override DataFlow::Node getInput() { result = this.getArgument(0) }
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/** No option for parsing */
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override predicate externalEntitiesEnabled() { none() }
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}
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/** Execution of a XPath statement. */
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private class RexmlXPathExecution extends XPathExecution::Range, DataFlow::CallNode {
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RexmlXPathExecution() {
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this =
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[API::getTopLevelMember("REXML").getMember("XPath"), API::getTopLevelMember("XPath")]
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.getAMethodCall(["each", "first", "match"])
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}
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override DataFlow::Node getXPath() { result = this.getArgument(1) }
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}
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}

‎ruby/ql/lib/codeql/ruby/security/XpathInjectionCustomizations.qll‎

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/**
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* Provides class and predicates to track external data that
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* may represent malicious xpath query objects.
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*
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* This module is intended to be imported into a taint-tracking query.
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*/
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private import codeql.ruby.Concepts
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private import codeql.ruby.DataFlow
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private import codeql.ruby.dataflow.BarrierGuards
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private import codeql.ruby.dataflow.RemoteFlowSources
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/** Models Xpath Injection related classes and functions */
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module XpathInjection {
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/** A data flow source for "XPath injection" vulnerabilities. */
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abstract class Source extends DataFlow::Node { }
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/** A data flow sink for "XPath injection" vulnerabilities */
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abstract class Sink extends DataFlow::Node { }
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/** A sanitizer for "XPath injection" vulnerabilities. */
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abstract class Sanitizer extends DataFlow::Node { }
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/**
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* A source of remote user input, considered as a flow source.
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*/
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private class RemoteFlowSourceAsSource extends Source, RemoteFlowSource { }
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/**
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* An execution of an XPath expression, considered as a sink.
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*/
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private class XPathExecutionAsSink extends Sink {
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XPathExecutionAsSink() { this = any(XPathExecution e).getXPath() }
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}
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/**
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* A construction of an XPath expression, considered as a sink.
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*/
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private class XPathConstructionAsSink extends Sink {
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XPathConstructionAsSink() { this = any(XPathConstruction c).getXPath() }
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}
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/**
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* A comparison with a constant string, considered as a sanitizer-guard.
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*/
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private class StringConstCompareAsSanitizerGuard extends Sanitizer, StringConstCompareBarrier { }
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/**
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* An inclusion check against an array of constant strings, considered as a
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* sanitizer-guard.
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*/
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private class StringConstArrayInclusionCallAsSanitizer extends Sanitizer,
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StringConstArrayInclusionCallBarrier { }
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}

‎ruby/ql/lib/codeql/ruby/security/XpathInjectionQuery.qll‎

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/**
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* Provides a taint-tracking configuration for detecting "Xpath Injection" vulnerabilities.
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*
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* Note, for performance reasons: only import this file if
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* `XpathInjection::Configuration` is needed, otherwise
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* `XpathInjectionCustomizations` should be imported instead.
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*/
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private import codeql.ruby.DataFlow
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private import codeql.ruby.TaintTracking
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import XpathInjectionCustomizations::XpathInjection
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/**
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* A taint-tracking configuration for detecting "Xpath Injection" vulnerabilities.
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*/
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class Configuration extends TaintTracking::Configuration {
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Configuration() { this = "Xpath Injection" }
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override predicate isSource(DataFlow::Node source) { source instanceof Source }
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override predicate isSink(DataFlow::Node source) { source instanceof Sink }
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override predicate isSanitizer(DataFlow::Node node) { node instanceof Sanitizer }
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}

‎ruby/ql/src/change-notes/2023-05-11-xpath-injection-query.md‎

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---
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category: newQuery
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---
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* Added a new experimental query, `rb/xpath-injection`, to detect cases where user input may be embedded into a template's code in an unsafe manner.

‎ruby/ql/src/experimental/xpath-injection/XpathInjection.qhelp‎

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<!DOCTYPE qhelp PUBLIC "-//Semmle//qhelp//EN" "qhelp.dtd">
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<qhelp>
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<overview>
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<p>
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If an XPath expression is built using string concatenation, and the components of the concatenation
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include user input, it makes it very easy for a user to create a malicious XPath expression.
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</p>
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</overview>
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<recommendation>
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<p>
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If user input must be included in an XPath expression, either sanitize the data or use variable
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references to safely embed it without altering the structure of the expression.
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</p>
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</recommendation>
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<example>
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<p>
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The following example uses the <code>nokogiri</code>, <code>rexml</code> and <code>libxml</code> XML parsers to parse a string <code>xml</code>.
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Then the xpath query is controlled by the user and hence leads to a vulnerability.
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</p>
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<sample src="examples/XPathBad.rb"/>
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<p>
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To guard against XPath Injection attacks, the user input should be sanitized.
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</p>
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<sample src="examples/XPathGood.rb"/>
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</example>
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<references>
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<li>
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OWASP:
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<a href="https://owasp.org/www-community/attacks/XPATH_Injection">XPath injection</a>.
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</li>
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</references>
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</qhelp>

‎ruby/ql/src/experimental/xpath-injection/XpathInjection.ql‎

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/**
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* @name XPath query built from user-controlled sources
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* @description Building a XPath query from user-controlled sources is vulnerable to insertion of
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* malicious Xpath code by the user.
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* @kind path-problem
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* @problem.severity error
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* @security-severity 9.8
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* @precision high
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* @id rb/xpath-injection
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* @tags security
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* external/cwe/cwe-643
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*/
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import codeql.ruby.DataFlow
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import codeql.ruby.security.XpathInjectionQuery
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import DataFlow::PathGraph
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from Configuration config, DataFlow::PathNode source, DataFlow::PathNode sink
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where config.hasFlowPath(source, sink)
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select sink.getNode(), source, sink, "XPath expression depends on a $@.", source.getNode(),
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"user-provided value"

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