/**
 * @name Disabled hostname verification
 * @description Marking a certificate as valid for a host without checking the certificate hostname allows an attacker to perform a machine-in-the-middle attack.
 * @kind path-problem
 * @problem.severity error
 * @precision high
 * @id java/insecure-hostname-verifier
 * @tags security
 *       external/cwe/cwe-297
 */

import java
import semmle.code.java.controlflow.Guards
import semmle.code.java.dataflow.DataFlow
import semmle.code.java.dataflow.FlowSources
import semmle.code.java.dataflow.TaintTracking2
import semmle.code.java.security.Encryption
import DataFlow::PathGraph

/**
 * Holds if `m` always returns `true` ignoring any exceptional flow.
 */
private predicate alwaysReturnsTrue(HostnameVerifierVerify m) {
  forex(ReturnStmt rs | rs.getEnclosingCallable() = m |
    rs.getResult().(CompileTimeConstantExpr).getBooleanValue() = true
  )
}

/**
 * A class that overrides the `javax.net.ssl.HostnameVerifier.verify` method and **always** returns `true` (though it could also exit due to an uncaught exception), thus
 * accepting any certificate despite a hostname mismatch.
 */
class TrustAllHostnameVerifier extends RefType {
  TrustAllHostnameVerifier() {
    this.getASupertype*() instanceof HostnameVerifier and
    exists(HostnameVerifierVerify m |
      m.getDeclaringType() = this and
      alwaysReturnsTrue(m)
    )
  }
}

/**
 * A configuration to model the flow of a `TrustAllHostnameVerifier` to a `set(Default)HostnameVerifier` call.
 */
class TrustAllHostnameVerifierConfiguration extends DataFlow::Configuration {
  TrustAllHostnameVerifierConfiguration() { this = "TrustAllHostnameVerifierConfiguration" }

  override predicate isSource(DataFlow::Node source) {
    source.asExpr().(ClassInstanceExpr).getConstructedType() instanceof TrustAllHostnameVerifier
  }

  override predicate isSink(DataFlow::Node sink) {
    exists(MethodAccess ma, Method m |
      (m instanceof SetDefaultHostnameVerifierMethod or m instanceof SetHostnameVerifierMethod) and
      ma.getMethod() = m
    |
      ma.getArgument(0) = sink.asExpr()
    )
  }
}

bindingset[result]
private string getAFlagName() {
  result.regexpMatch("(?i).*(secure|(en|dis)able|selfCert|selfSign|validat|verif|trust|ignore).*")
}

/** A configuration to model the flow of feature flags into `Guard`s. This is used to determine whether something is guarded by such a flag. */
private class FlagTaintTracking extends TaintTracking2::Configuration {
  FlagTaintTracking() { this = "FlagTaintTracking" }

  override predicate isSource(DataFlow::Node source) {
    exists(VarAccess v | v.getVariable().getName() = getAFlagName() | source.asExpr() = v)
    or
    exists(StringLiteral s | s.getRepresentedString() = getAFlagName() | source.asExpr() = s)
    or
    exists(MethodAccess ma | ma.getMethod().getName() = getAFlagName() | source.asExpr() = ma)
  }

  override predicate isSink(DataFlow::Node sink) { sink.asExpr() instanceof Guard }

  override predicate isAdditionalTaintStep(DataFlow::Node node1, DataFlow::Node node2) {
    exists(MethodAccess ma | ma.getMethod() = any(EnvTaintedMethod m) |
      ma = node2.asExpr() and ma.getAnArgument() = node1.asExpr()
    )
    or
    exists(MethodAccess ma |
      ma.getMethod().hasName("parseBoolean") and
      ma.getMethod().getDeclaringType().hasQualifiedName("java.lang", "Boolean")
    |
      ma = node2.asExpr() and ma.getAnArgument() = node1.asExpr()
    )
  }
}

/** Gets a guard that depends on a flag. */
private Guard getAGuard() {
  exists(FlagTaintTracking cfg, DataFlow::Node source, DataFlow::Node sink |
    cfg.hasFlow(source, sink)
  |
    sink.asExpr() = result
  )
}

/** Holds if `node` is guarded by a flag that suggests an intentionally insecure feature. */
private predicate isNodeGuardedByFlag(DataFlow::Node node) {
  exists(Guard g | g.controls(node.asExpr().getBasicBlock(), _) | g = getAGuard())
}

from
  DataFlow::PathNode source, DataFlow::PathNode sink, TrustAllHostnameVerifierConfiguration cfg,
  RefType verifier
where
  cfg.hasFlowPath(source, sink) and
  not isNodeGuardedByFlag(sink.getNode()) and
  verifier = source.getNode().asExpr().(ClassInstanceExpr).getConstructedType()
select sink, source, sink,
  "$@ that is defined $@ and accepts any certificate as valid, is used here.", source,
  "This hostname verifier", verifier, "here"