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Merge pull request #2330 from erik-krogh/exceptionXss
JS: Added query for detecting XSS that happens through an exception
2 parents 73e08eb + 9351cd4 commit f958916

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‎change-notes/1.24/analysis-javascript.md‎

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## New queries
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| **Query** | **Tags** | **Purpose** |
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|---------------------------------------------------------------------------|-------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| **Query** | **Tags** | **Purpose** |
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|---------------------------------------------------------------------------------|-------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| Cross-site scripting through exception (`js/xss-through-exception`) | security, external/cwe/cwe-079, external/cwe/cwe-116 | Highlights potential XSS vulnerabilities where an exception is written to the DOM. Results are not shown on LGTM by default. |
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## Changes to existing queries
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‎javascript/ql/src/Security/CWE-079/ExceptionXss.qhelp‎

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<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>
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Directly writing exceptions to a webpage without sanitization allows for a cross-site scripting
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vulnerability if the value of the exception can be influenced by a user.
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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 guard against cross-site scripting, consider using contextual output encoding/escaping before
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writing user input to the page, or one of the other solutions that are mentioned in the
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references.
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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 shows an exception being written directly to the document,
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and this exception can potentially be influenced by the page URL,
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leaving the website vulnerable to cross-site scripting.
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</p>
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<sample src="examples/ExceptionXss.js" />
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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://cheatsheetseries.owasp.org/cheatsheets/DOM_based_XSS_Prevention_Cheat_Sheet.html">DOM based
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XSS Prevention Cheat Sheet</a>.
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</li>
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<li>
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OWASP:
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<a href="https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html">XSS
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(Cross Site Scripting) Prevention Cheat Sheet</a>.
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</li>
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<li>
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OWASP
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<a href="https://www.owasp.org/index.php/DOM_Based_XSS">DOM Based XSS</a>.
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</li>
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<li>
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OWASP
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<a href="https://www.owasp.org/index.php/Types_of_Cross-Site_Scripting">Types of Cross-Site
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Scripting</a>.
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</li>
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<li>
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Wikipedia: <a href="http://en.wikipedia.org/wiki/Cross-site_scripting">Cross-site scripting</a>.
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</li>
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</references>
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</qhelp>

‎javascript/ql/src/Security/CWE-079/ExceptionXss.ql‎

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/**
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* @name Cross-site scripting through exception
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* @description Inserting data from an exception containing user
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* input into the DOM may enable cross-site scripting.
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* @kind path-problem
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* @problem.severity error
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* @precision medium
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* @id js/xss-through-exception
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* @tags security
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* external/cwe/cwe-079
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* external/cwe/cwe-116
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*/
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import javascript
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import semmle.javascript.security.dataflow.ExceptionXss::ExceptionXss
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import DataFlow::PathGraph
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from
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Configuration cfg, DataFlow::PathNode source, DataFlow::PathNode sink
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where
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cfg.hasFlowPath(source, sink)
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select sink.getNode(), source, sink,
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sink.getNode().(Xss::Shared::Sink).getVulnerabilityKind() + " vulnerability due to $@.", source.getNode(),
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"user-provided value"

‎javascript/ql/src/Security/CWE-079/examples/ExceptionXss.js‎

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function setLanguageOptions() {
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var href = document.location.href,
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deflt = href.substring(href.indexOf("default=")+8);
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try {
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var parsed = unknownParseFunction(deflt);
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} catch(e) {
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document.write("Had an error: " + e + ".");
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}
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}

‎javascript/ql/src/semmle/javascript/Expr.qll‎

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@@ -245,6 +245,21 @@ class Expr extends @expr, ExprOrStmt, ExprOrType, AST::ValueNode {
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ctx.(ConditionalExpr).inNullSensitiveContext()
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)
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}
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/**
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* Gets the data-flow node where exceptions thrown by this expression will
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* propagate if this expression causes an exception to be thrown.
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*/
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DataFlow::Node getExceptionTarget() {
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if exists(this.getEnclosingStmt().getEnclosingTryCatchStmt())
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then
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result = DataFlow::parameterNode(this
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.getEnclosingStmt()
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.getEnclosingTryCatchStmt()
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.getACatchClause()
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.getAParameter())
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else result = any(DataFlow::FunctionNode f | f.getFunction() = this.getContainer()).getExceptionalReturn()
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}
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}
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/**

‎javascript/ql/src/semmle/javascript/Stmt.qll‎

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}
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override predicate isAmbient() { hasDeclareKeyword(this) or getParent().isAmbient() }
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/**
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* Gets the `try` statement with a catch block containing this statement without
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* crossing function boundaries or other `try ` statements with catch blocks.
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*/
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TryStmt getEnclosingTryCatchStmt() {
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getParentStmt+() = result.getBody() and
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exists(result.getACatchClause()) and
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not exists(TryStmt mid | exists(mid.getACatchClause()) |
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getParentStmt+() = mid.getBody() and mid.getParentStmt+() = result.getBody()
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)
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}
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}
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/**

‎javascript/ql/src/semmle/javascript/dataflow/Configuration.qll‎

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// Skip to the top of big left-leaning string concatenation trees.
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nd = any(AddExpr add).flow() and
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nd = any(AddExpr add).getAnOperand().flow()
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or
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// Skip the exceptional return on functions, as this highlights the entire function.
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nd = any(DataFlow::FunctionNode f).getExceptionalReturn()
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}
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}
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‎javascript/ql/src/semmle/javascript/dataflow/TaintTracking.qll‎

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succ = this
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}
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}
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/**
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* A taint propagating data flow edge arising from calling `String.prototype.match()`.
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*/
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private class StringMatchTaintStep extends AdditionalTaintStep, DataFlow::MethodCallNode {
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StringMatchTaintStep() {
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this.getMethodName() = "match" and
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this.getNumArgument() = 1 and
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this.getArgument(0) .analyze().getAType() = TTRegExp()
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}
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override predicate step(DataFlow::Node pred, DataFlow::Node succ) {
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pred = this.getReceiver() and
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succ = this
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}
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}
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/**
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* A taint propagating data flow edge arising from JSON unparsing.

‎javascript/ql/src/semmle/javascript/dataflow/internal/FlowSteps.qll‎

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@@ -66,19 +66,7 @@ predicate localExceptionStep(DataFlow::Node pred, DataFlow::Node succ) {
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or
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DataFlow::exceptionalInvocationReturnNode(pred, expr)
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|
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// Propagate out of enclosing function.
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not exists(getEnclosingTryStmt(expr.getEnclosingStmt())) and
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exists(Function f |
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f = expr.getEnclosingFunction() and
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DataFlow::exceptionalFunctionReturnNode(succ, f)
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)
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or
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// Propagate to enclosing try/catch.
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// To avoid false flow, we only propagate to an unguarded catch clause.
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exists(TryStmt try |
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try = getEnclosingTryStmt(expr.getEnclosingStmt()) and
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DataFlow::parameterNode(succ, try.getCatchClause().getAParameter())
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)
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succ = expr.getExceptionTarget()
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)
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}
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cached
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predicate callStep(DataFlow::Node pred, DataFlow::Node succ) { argumentPassing(_, pred, _, succ) }
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/**
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* Gets the `try` statement containing `stmt` without crossing function boundaries
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* or other `try ` statements.
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*/
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cached
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TryStmt getEnclosingTryStmt(Stmt stmt) {
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result.getBody() = stmt
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or
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not stmt instanceof Function and
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not stmt = any(TryStmt try).getBody() and
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result = getEnclosingTryStmt(stmt.getParentStmt())
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}
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/**
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* Holds if there is a flow step from `pred` to `succ` through:
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* - returning a value from a function call, or

‎javascript/ql/src/semmle/javascript/security/dataflow/DomBasedXss.qll‎

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import javascript
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module DomBasedXss {
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import Xss::DomBasedXss
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import DomBasedXssCustomizations::DomBasedXss
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/**
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* A taint-tracking configuration for reasoning about XSS.
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node instanceof Sanitizer
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}
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}
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/** A source of remote user input, considered as a flow source for DOM-based XSS. */
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class RemoteFlowSourceAsSource extends Source {
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RemoteFlowSourceAsSource() { this instanceof RemoteFlowSource }
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}
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/**
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* An access of the URL of this page, or of the referrer to this page.
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*/
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class LocationSource extends Source {
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LocationSource() { this = DOM::locationSource() }
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}
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}

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