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Merge pull request github#12311 from maikypedia/maikypedia/ruby-ssti
Ruby: Add Server Side Template Injection query
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‎ruby/ql/lib/codeql/ruby/Concepts.qll

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@@ -1063,3 +1063,69 @@ module Cryptography {
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class BlockMode = SC::BlockMode;
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}
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/**
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* A data-flow node that constructs a template.
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*
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* Often, it is worthy of an alert if a template is constructed such that
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* executing it would be a security risk.
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*
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* If it is important that the template is rendered, use `TemplateRendering`.
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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 `TemplateConstruction::Range` instead.
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*/
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class TemplateConstruction extends DataFlow::Node instanceof TemplateConstruction::Range {
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/** Gets the argument that specifies the template to be constructed. */
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DataFlow::Node getTemplate() { result = super.getTemplate() }
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}
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/** Provides a class for modeling new template rendering APIs. */
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module TemplateConstruction {
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/**
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* A data-flow node that constructs a template.
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*
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* Often, it is worthy of an alert if a template is constructed such that
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* executing it would be a security risk.
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*
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* If it is important that the template is rendered, use `TemplateRendering`.
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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 `TemplateConstruction` 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 template to be constructed. */
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abstract DataFlow::Node getTemplate();
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}
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}
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/**
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* A data-flow node that renders templates.
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*
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* If the context of interest is such that merely constructing a template
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* would be valuable to report, consider using `TemplateConstruction`.
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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 `TemplateRendering::Range` instead.
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*/
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class TemplateRendering extends DataFlow::Node instanceof TemplateRendering::Range {
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/** Gets the argument that specifies the template to be rendered. */
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DataFlow::Node getTemplate() { result = super.getTemplate() }
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}
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/** Provides a class for modeling new template rendering APIs. */
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module TemplateRendering {
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/**
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* A data-flow node that renders templates.
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*
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* If the context of interest is such that merely constructing a template
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* would be valuable to report, consider using `TemplateConstruction`.
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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 `TemplateRendering` 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 template to be rendered. */
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abstract DataFlow::Node getTemplate();
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}
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}

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

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@@ -27,5 +27,7 @@ private import codeql.ruby.frameworks.ActionDispatch
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private import codeql.ruby.frameworks.PosixSpawn
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private import codeql.ruby.frameworks.StringFormatters
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private import codeql.ruby.frameworks.Json
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private import codeql.ruby.frameworks.Erb
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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

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

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/**
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* Provides templating for embedding Ruby code into text files, allowing dynamic content generation in web applications.
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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 templating for embedding Ruby code into text files, allowing dynamic content generation in web applications.
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*/
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module Erb {
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/**
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* Flow summary for `ERB.new`. This method wraps a template string, compiling it.
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*/
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private class TemplateSummary extends SummarizedCallable {
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TemplateSummary() { this = "ERB.new" }
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override MethodCall getACall() { result = any(ErbTemplateNewCall 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 `ERB.new`, considered as a template construction. */
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private class ErbTemplateNewCall extends TemplateConstruction::Range, DataFlow::CallNode {
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ErbTemplateNewCall() { this = API::getTopLevelMember("ERB").getAnInstantiation() }
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override DataFlow::Node getTemplate() { result = this.getArgument(0) }
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}
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/** A call to `ERB.new(foo).result(binding)`, considered as a template rendering. */
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private class ErbTemplateRendering extends TemplateRendering::Range, DataFlow::CallNode {
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private DataFlow::Node template;
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ErbTemplateRendering() {
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exists(ErbTemplateNewCall templateConstruction |
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this = templateConstruction.getAMethodCall("result") and
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template = templateConstruction.getTemplate()
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)
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}
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override DataFlow::Node getTemplate() { result = template }
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}
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}

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

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/**
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* Provides templating for embedding Ruby code into text files, allowing dynamic content generation in web applications.
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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 templating for embedding Ruby code into text files, allowing dynamic content generation in web applications.
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*/
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module Slim {
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/** A call to `Slim::Template.new`, considered as a template construction. */
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private class SlimTemplateNewCall extends TemplateConstruction::Range, DataFlow::CallNode {
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SlimTemplateNewCall() {
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this = API::getTopLevelMember("Slim").getMember("Template").getAnInstantiation()
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}
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override DataFlow::Node getTemplate() {
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result.asExpr().getExpr() =
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this.getBlock().(DataFlow::BlockNode).asCallableAstNode().getAStmt()
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}
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}
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/** A call to `Slim::Template.new{ foo }.render`, considered as a template rendering */
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private class SlimTemplateRendering extends TemplateRendering::Range, DataFlow::CallNode {
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private DataFlow::Node template;
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SlimTemplateRendering() {
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exists(SlimTemplateNewCall templateConstruction |
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this = templateConstruction.getAMethodCall("render") and
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template = templateConstruction.getTemplate()
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)
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}
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override DataFlow::Node getTemplate() { result = template }
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}
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}

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

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/**
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* Provides default sources, sinks and sanitizers for detecting
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* ERB Server Side Template Injections, as well as extension points for adding your own
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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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/**
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* Provides default sources, sinks and sanitizers for detecting
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* Server Side Template Injections, as well as extension points for adding your own
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*/
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module TemplateInjection {
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/** A data flow source for SSTI vulnerabilities */
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abstract class Source extends DataFlow::Node { }
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/** A data flow sink for SSTI vulnerabilities */
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abstract class Sink extends DataFlow::Node { }
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/** A sanitizer for SSTI 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 Server Side Template Injection rendering, considered as a flow sink.
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*/
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private class TemplateRenderingAsSink extends Sink {
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TemplateRenderingAsSink() { this = any(TemplateRendering e).getTemplate() }
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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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{ }
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}

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

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/**
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* Provides default sources, sinks and sanitizers for detecting
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* Server Side Template Injections, as well as extension points for adding your own
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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 TemplateInjectionCustomizations::TemplateInjection
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/**
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* A taint-tracking configuration for detecting Server Side Template Injections vulnerabilities.
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*/
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class Configuration extends TaintTracking::Configuration {
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Configuration() { this = "TemplateInjection" }
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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/2023-03-15-ssti-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/server-side-template-injection`, to detect cases where user input may be embedded into a template's code in an unsafe manner.

‎ruby/ql/src/experimental/template-injection/TemplateInjection.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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Template Injection occurs when user input is embedded in a template's code in an unsafe manner.
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An attacker can use native template syntax to inject a malicious payload into a template, which is then executed server-side.
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This permits the attacker to run arbitrary code in the server's context.
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</p>
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</overview>
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<recommendation>
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<p>
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To fix this, ensure that untrusted input is not used as part of a template's code. If the application requirements do not allow this,
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use a sandboxed environment where access to unsafe attributes and methods is prohibited.
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</p>
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</recommendation>
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<example>
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<p>
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Consider the example given below, an untrusted HTTP parameter <code>name</code> is used to generate a template string. This can lead to remote code execution.
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</p>
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<sample src="examples/SSTIBad.rb" />
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<p>
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Here we have fixed the problem by including ERB/Slim syntax in the string, then the user input will be rendered but not evaluated.
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</p>
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<sample src="examples/SSTIGood.rb" />
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</example>
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<references>
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<li>
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Wikipedia: <a href="https://en.wikipedia.org/wiki/Code_injection#Server_Side_Template_Injection">Server Side Template Injection</a>.
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</li>
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<li>
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Portswigger : <a href="https://portswigger.net/web-security/server-side-template-injection">Server Side Template Injection</a>.
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</li>
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</references>
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</qhelp>

‎ruby/ql/src/experimental/template-injection/TemplateInjection.ql

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/**
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* @name Server-side template injection
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* @description Building a server-side template from user-controlled sources is vulnerable to
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* insertion of malicious code by the user.
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* @kind path-problem
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* @problem.severity error
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* @security-severity 8.8
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* @precision high
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* @id rb/server-side-template-injection
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* @tags security
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* external/cwe/cwe-94
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*/
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import codeql.ruby.DataFlow
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import codeql.ruby.security.TemplateInjectionQuery
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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, "This template depends on a $@.", source.getNode(),
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"user-provided value"

‎ruby/ql/src/experimental/template-injection/examples/SSTIBad.rb

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require 'erb'
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require 'slim'
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class BadERBController < ActionController::Base
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def some_request_handler
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name = params["name"]
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html_text = "
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<!DOCTYPE html><html><body>
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<h2>Hello %s </h2></body></html>
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" % name
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template = ERB.new(html_text).result(binding)
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end
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end
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class BadSlimController < ActionController::Base
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def some_request_handler
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name = params["name"]
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html_text = "
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<!DOCTYPE html><html><body>
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<h2>Hello %s </h2></body></html>
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" % name
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Slim::Template.new{ html_text }.render
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end
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end

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