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initial query, insecure random to sensitive sinks
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‎powershell/ql/lib/semmle/code/powershell/security/InsecureRandomnessCustomizations.qll‎

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/**
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* Provides default sources, sinks and sanitizers for reasoning about
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* insecure-randomness vulnerabilities, as well as extension points for
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* adding your own.
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*/
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private import semmle.code.powershell.dataflow.DataFlow
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import semmle.code.powershell.ApiGraphs
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module InsecureRandomness {
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/**
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* A data flow source for insecure-randomness vulnerabilities.
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*/
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abstract class Source extends DataFlow::Node { }
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/**
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* A data flow sink for insecure-randomness vulnerabilities.
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*/
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abstract class Sink extends DataFlow::Node {
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/** Gets a human-readable description of this sink. */
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abstract string getSinkDescription();
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}
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/**
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* A sanitizer for insecure-randomness vulnerabilities.
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*/
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abstract class Sanitizer extends DataFlow::Node { }
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/** A call to the `Get-Random` cmdlet. */
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class GetRandomSource extends Source instanceof DataFlow::CallNode {
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GetRandomSource() { this.matchesName("Get-Random") }
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}
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/** An instantiation of `System.Random` via `New-Object`. */
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class SystemRandomObjectCreation extends Source instanceof DataFlow::ObjectCreationNode {
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SystemRandomObjectCreation() {
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this.asExpr()
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.getExpr()
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.(ObjectCreation)
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.getAnArgument()
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.getValue()
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.stringMatches("System.Random")
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}
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}
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/** A call to `[System.Random]::new()` via the API graph. */
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class SystemRandomNewCall extends Source instanceof DataFlow::CallNode {
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SystemRandomNewCall() {
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this = API::getTopLevelMember("system").getMember("random").getMember("new").asCall()
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}
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}
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/** Assignment to .Key or .IV on an object. */
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class CryptoKeyIvAssignmentSink extends Sink {
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CryptoKeyIvAssignmentSink() {
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exists(AssignStmt a, MemberExprWriteAccess m |
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m = a.getLeftHandSide() and
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m.getLowerCaseMemberName() in ["key", "iv"] and
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this.asExpr().getExpr() = a.getRightHandSide()
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)
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}
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override string getSinkDescription() { result = "a cryptographic key or IV" }
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}
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/** Argument to a cryptographic constructor (HMAC key or KDF salt). */
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class CryptoConstructorSink extends Sink {
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CryptoConstructorSink() {
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exists(DataFlow::ObjectCreationNode oc |
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(
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oc.getLowerCaseConstructedTypeName().matches("%hmac%")
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or
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oc.getLowerCaseConstructedTypeName().matches("%rfc2898derivebytes%")
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) and
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this = oc.getAnArgument() and
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not this = oc.getConstructedTypeNode()
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)
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}
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override string getSinkDescription() { result = "a cryptographic operation" }
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}
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/** First positional argument to ConvertTo-SecureString. */
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class SecureStringSink extends Sink {
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SecureStringSink() {
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exists(DataFlow::CallNode call |
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call.matchesName("ConvertTo-SecureString") and
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this = call.getPositionalArgument(0)
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)
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}
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override string getSinkDescription() { result = "a secure string conversion" }
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}
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/** Value used in HTTP headers passed to Invoke-RestMethod or Invoke-WebRequest. */
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class HttpHeaderValueSink extends Sink {
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HttpHeaderValueSink() {
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exists(DataFlow::CallNode call, HashTableExpr ht |
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(call.matchesName("Invoke-RestMethod") or call.matchesName("Invoke-WebRequest")) and
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call.getNamedArgument("headers").asExpr().getExpr() = ht and
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this.asExpr().getExpr() = ht.getAValue()
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)
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}
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override string getSinkDescription() { result = "an HTTP header" }
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}
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}

‎powershell/ql/lib/semmle/code/powershell/security/InsecureRandomnessQuery.qll‎

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/**
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* Provides a taint tracking configuration for reasoning about
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* insecure-randomness vulnerabilities (CWE-338).
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*
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* Note, for performance reasons: only import this file if
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* `InsecureRandomnessFlow` is needed, otherwise
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* `InsecureRandomnessCustomizations` should be imported instead.
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*/
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import powershell
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import semmle.code.powershell.dataflow.TaintTracking
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import InsecureRandomnessCustomizations::InsecureRandomness
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import semmle.code.powershell.dataflow.DataFlow
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private module Config implements DataFlow::ConfigSig {
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predicate isSource(DataFlow::Node source) { source instanceof Source }
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predicate isSink(DataFlow::Node sink) { sink instanceof Sink }
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predicate isBarrier(DataFlow::Node node) { node instanceof Sanitizer }
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predicate isAdditionalFlowStep(DataFlow::Node node1, DataFlow::Node node2) {
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// When .NextBytes() is called on a System.Random instance,
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// taint flows from the qualifier to the argument (the byte array is filled with random bytes).
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exists(DataFlow::CallNode call |
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call.matchesName("NextBytes") and
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node1 = call.getQualifier() and
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node2.(DataFlow::PostUpdateNode).getPreUpdateNode() = call.getArgument(0)
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)
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}
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}
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/**
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* Taint-tracking for reasoning about insecure-randomness vulnerabilities.
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*/
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module InsecureRandomnessFlow = TaintTracking::Global<Config>;

‎powershell/ql/src/queries/security/cwe-338/InsecureRandomness.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>Using non-cryptographic random number generators for security-sensitive operations can compromise security. `Get-Random` and `System.Random` are not suitable for generating cryptographic keys, security tokens, or other security-critical random values.</p>
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</overview>
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<recommendation>
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<p>Use a cryptographically secure random number generator such as `[System.Security.Cryptography.RandomNumberGenerator]` instead.</p>
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</recommendation>
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<example>
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<p>Insecure random:</p>
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<sample src="examples/InsecureRandomness/InsecureRandomnessBad.ps1" />
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<p>Secure alternative:</p>
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<sample src="examples/InsecureRandomness/InsecureRandomnessGood.ps1" />
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</example>
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<references>
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<li><a href="https://cwe.mitre.org/data/definitions/338.html">CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)</a>.</li>
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<li><a href="https://learn.microsoft.com/en-us/dotnet/api/system.security.cryptography.randomnumbergenerator">System.Security.Cryptography.RandomNumberGenerator</a>.</li>
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</references>
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</qhelp>

‎powershell/ql/src/queries/security/cwe-338/InsecureRandomness.ql‎

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/**
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* @name Use of insecure random number generator
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* @name Use of insecure random number generator in security-sensitive context
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* @description Using non-cryptographic random number generators such as Get-Random or System.Random
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* for security-sensitive operations can compromise security.
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* @kind problem
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* @kind path-problem
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* @problem.severity error
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* @security-severity 7.5
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* @precision high
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* @id powershell/microsoft/security/insecure-random
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* @id powershell/insecure-randomness
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* @tags security
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* external/cwe/cwe-330
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* external/cwe/cwe-338
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*/
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import powershell
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import semmle.code.powershell.ApiGraphs
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import semmle.code.powershell.dataflow.DataFlow
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import semmle.code.powershell.security.InsecureRandomnessQuery
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import InsecureRandomnessFlow::PathGraph
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/** A call to the `Get-Random` cmdlet. */
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class GetRandomCall extends DataFlow::CallNode {
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GetRandomCall() { this.matchesName("Get-Random") }
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}
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/** An instantiation of `System.Random` via `New-Object`. */
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class SystemRandomObjectCreation extends DataFlow::ObjectCreationNode {
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SystemRandomObjectCreation() {
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this.asExpr()
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.getExpr()
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.(ObjectCreation)
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.getAnArgument()
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.getValue()
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.stringMatches("System.Random")
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}
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}
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/** A call to `[System.Random]::new()` via the API graph. */
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class SystemRandomNewCall extends DataFlow::CallNode {
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SystemRandomNewCall() {
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this = API::getTopLevelMember("system").getMember("random").getMember("new").asCall()
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}
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}
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from DataFlow::Node node, string msg
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where
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node instanceof GetRandomCall and
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msg =
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"Use of insecure random number generator 'Get-Random'. Use [System.Security.Cryptography.RandomNumberGenerator] instead."
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or
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node instanceof SystemRandomObjectCreation and
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msg =
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"Use of insecure random number generator 'System.Random'. Use [System.Security.Cryptography.RandomNumberGenerator] instead."
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or
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node instanceof SystemRandomNewCall and
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msg =
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"Use of insecure random number generator 'System.Random'. Use [System.Security.Cryptography.RandomNumberGenerator] instead."
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select node, msg
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from InsecureRandomnessFlow::PathNode source, InsecureRandomnessFlow::PathNode sink
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where InsecureRandomnessFlow::flowPath(source, sink)
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select sink.getNode(), source, sink,
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"Insecure random value flows to " + sink.getNode().(Sink).getSinkDescription() + " from $@.",
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source.getNode(), "this insecure random source"

‎powershell/ql/src/queries/security/cwe-338/examples/InsecureRandomness/InsecureRandomnessBad.ps1‎

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# BAD: weak RNG output flows into security-sensitive .NET crypto sinks.
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# 1) Weak bytes flow into AES .Key and .IV properties
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$weak = New-Object System.Random
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$keyBytes = New-Object byte[] 32
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$ivBytes = New-Object byte[] 16
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$weak.NextBytes($keyBytes)
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$weak.NextBytes($ivBytes)
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$aes = [System.Security.Cryptography.Aes]::Create()
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$aes.Key = $keyBytes # BAD: predictable key
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$aes.IV = $ivBytes # BAD: predictable IV
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# 2) Weak bytes flow into HMAC constructor (signing key)
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$hmacKeyBytes = New-Object byte[] 64
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$weak.NextBytes($hmacKeyBytes)
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$hmac = New-Object System.Security.Cryptography.HMACSHA256(,$hmacKeyBytes) # BAD: predictable HMAC key
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# 3) Weak bytes used as salt for password-based key derivation
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$saltBytes = New-Object byte[] 8
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$weak.NextBytes($saltBytes)
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$kdf = New-Object System.Security.Cryptography.Rfc2898DeriveBytes("password", $saltBytes) # BAD: predictable salt
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# 4) Get-Random result flows into ConvertTo-SecureString → PSCredential
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$tempPwd = (Get-Random -Maximum 999999999).ToString()
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$securePwd = ConvertTo-SecureString $tempPwd -AsPlainText -Force
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$cred = New-Object System.Management.Automation.PSCredential("admin", $securePwd) # BAD: predictable credential
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# 5) Weak random flows into HTTP Authorization header
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$tokenValue = Get-Random -Maximum 999999999
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Invoke-RestMethod -Uri "https://api.example.com/data" `
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-Headers @{ Authorization = "Bearer $tokenValue" } # BAD: predictable bearer token
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# 6) Weak random used as RNGCryptoServiceProvider substitute for key bytes
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$rng2 = [System.Random]::new()
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$aesKey2 = New-Object byte[] 32
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$rng2.NextBytes($aesKey2)
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[Security.Cryptography.RNGCryptoServiceProvider]::Create().GetBytes($aesKey2) | Out-Null
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# The above line re-fills the buffer, but the initial weak fill might persist
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# if code logic is wrong. True BAD pattern: relying solely on System.Random:
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$aes2 = [System.Security.Cryptography.Aes]::Create()
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$rng2.NextBytes($aesKey2) # BAD: final value comes from weak RNG
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$aes2.Key = $aesKey2 # BAD: predictable key assigned to cipher

‎powershell/ql/src/queries/security/cwe-338/examples/InsecureRandomness/InsecureRandomnessGood.ps1‎

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# GOOD: cryptographic RNG output flows into security-sensitive .NET crypto sinks.
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# 1) CSPRNG bytes flow into AES .Key and .IV properties
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$keyBytes = New-Object byte[] 32
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$ivBytes = New-Object byte[] 16
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[System.Security.Cryptography.RandomNumberGenerator]::Fill($keyBytes)
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[System.Security.Cryptography.RandomNumberGenerator]::Fill($ivBytes)
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$aes = [System.Security.Cryptography.Aes]::Create()
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$aes.Key = $keyBytes # GOOD: cryptographically random key
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$aes.IV = $ivBytes # GOOD: cryptographically random IV
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# 2) CSPRNG bytes flow into HMAC constructor (signing key)
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$hmacKeyBytes = New-Object byte[] 64
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[System.Security.Cryptography.RandomNumberGenerator]::Fill($hmacKeyBytes)
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$hmac = New-Object System.Security.Cryptography.HMACSHA256(,$hmacKeyBytes) # GOOD
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# 3) CSPRNG bytes used as salt for password-based key derivation
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$saltBytes = New-Object byte[] 16
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[System.Security.Cryptography.RandomNumberGenerator]::Fill($saltBytes)
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$kdf = New-Object System.Security.Cryptography.Rfc2898DeriveBytes("password", $saltBytes) # GOOD
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# 4) CSPRNG bytes flow into ConvertTo-SecureString → PSCredential
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$pwdBytes = New-Object byte[] 32
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[System.Security.Cryptography.RandomNumberGenerator]::Fill($pwdBytes)
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$tempPwd = [Convert]::ToBase64String($pwdBytes)
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$securePwd = ConvertTo-SecureString $tempPwd -AsPlainText -Force
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$cred = New-Object System.Management.Automation.PSCredential("admin", $securePwd) # GOOD
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# 5) CSPRNG bytes flow into HTTP Authorization header
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$tokenBytes = New-Object byte[] 32
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[System.Security.Cryptography.RandomNumberGenerator]::Fill($tokenBytes)
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$bearerToken = [Convert]::ToBase64String($tokenBytes)
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Invoke-RestMethod -Uri "https://api.example.com/data" `
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-Headers @{ Authorization = "Bearer $bearerToken" } # GOOD
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# 6) CSPRNG via RNGCryptoServiceProvider fills key bytes for cipher
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$rng = [Security.Cryptography.RNGCryptoServiceProvider]::Create()
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$aesKey2 = New-Object byte[] 32
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$rng.GetBytes($aesKey2) # GOOD: filled by CSPRNG
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$aes2 = [System.Security.Cryptography.Aes]::Create()
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$aes2.Key = $aesKey2 # GOOD: unpredictable key

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