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CWE-322 InsecureHostKeyCallback (#234)
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‎ql/src/experimental/CWE-322/InsecureHostKeyCallback.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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The <code>ClientConfig</code> specifying the configuration for establishing a SSH connection has a field <code>HostKeyCallback</code> that must be initialized with a function that validates the host key returned by the server.
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</p>
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<p>
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Not properly verifying the host key returned by a server provides attackers with an opportunity to perform a Machine-in-the-Middle (MitM) attack.
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A successful attack can compromise the confidentiality and integrity of the information communicated with the server.
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</p>
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<p>
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The <code>ssh</code> package provides the predefined callback <code>InsecureIgnoreHostKey</code> that can be used during development and testing.
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It accepts any provided host key.
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This callback, or a semantically similar callback, should not be used in production code.
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</p>
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</overview>
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<recommendation>
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<p>
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The <code>HostKeyCallback</code> field of <code>ClientConfig</code> should be initialized with a function that validates a host key against an allow list.
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If a key is not on a predefined allow list, the connection must be terminated and the failed security operation should be logged.
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</p>
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<p>
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When the allow list contains only a single host key then the function <code>FixedHostKey</code> can be used.
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</p>
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</recommendation>
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<example>
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<p>The following example shows the use of <code>InsecureIgnoreHostKey</code> and an insecure host key callback implemention commonly used in non-production code.</p>
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<sample src="InsecureHostKeyCallbackExample.go" />
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<p>The next example shows a secure implementation using the <code>FixedHostKey</code> that implements an allow-list.</p>
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<sample src="SecureHostKeyCallbackExample.go" />
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</example>
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<references>
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<li>
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Go Dev:
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<a href="https://pkg.go.dev/golang.org/x/crypto/ssh?tab=doc">package ssh</a>.
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</li>
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</references>
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</qhelp>

‎ql/src/experimental/CWE-322/InsecureHostKeyCallback.ql‎

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/**
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* @name Use of insecure HostKeyCallback implementation
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* @description Detects insecure SSL client configurations with an implementation of the `HostKeyCallback` that accepts all host keys.
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* @kind path-problem
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* @problem.severity error
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* @precision very-high
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* @id go/insecure-hostkeycallback
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* @tags security
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*/
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import go
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import DataFlow::PathGraph
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class InsecureIgnoreHostKey extends Function {
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InsecureIgnoreHostKey() {
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this.hasQualifiedName("golang.org/x/crypto/ssh", "InsecureIgnoreHostKey")
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}
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}
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/** A callback function value that is insecure when used as a `HostKeyCallback`, because it always returns `nil`. */
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class InsecureHostKeyCallbackFunc extends DataFlow::Node {
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InsecureHostKeyCallbackFunc() {
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// Either a call to InsecureIgnoreHostKey(), which we know returns an insecure callback.
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this = any(InsecureIgnoreHostKey f).getACall()
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or
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// Or a callback function in the source code (named or anonymous) that always returns nil.
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forex(DataFlow::ResultNode returnValue |
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returnValue = this.(DataFlow::FunctionNode).getAResult()
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|
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returnValue = Builtin::nil().getARead()
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)
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}
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}
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class HostKeyCallbackAssignmentConfig extends DataFlow::Configuration {
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HostKeyCallbackAssignmentConfig() { this = "HostKeyCallbackAssignmentConfig" }
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override predicate isSource(DataFlow::Node source) {
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source instanceof InsecureHostKeyCallbackFunc
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}
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override predicate isSink(DataFlow::Node sink) {
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exists(Field f |
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f.hasQualifiedName("golang.org/x/crypto/ssh", "ClientConfig", "HostKeyCallback") and
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sink = f.getAWrite().getRhs()
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)
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}
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}
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from HostKeyCallbackAssignmentConfig config, DataFlow::PathNode source, DataFlow::PathNode sink
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where config.hasFlowPath(source, sink)
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select sink, source, sink,
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"Configuring SSH ClientConfig with insecure HostKeyCallback implementation from $@.",
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source.getNode(), "this source"

‎ql/src/experimental/CWE-322/InsecureHostKeyCallbackExample.go‎

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package main
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import (
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"golang.org/x/crypto/ssh"
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"net"
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)
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func main() {}
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func insecureIgnoreHostKey() {
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_ = &ssh.ClientConfig{
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User: "username",
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Auth: []ssh.AuthMethod{nil},
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HostKeyCallback: ssh.InsecureIgnoreHostKey(),
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}
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}
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func insecureHostKeyCallback() {
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_ = &ssh.ClientConfig{
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User: "username",
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Auth: []ssh.AuthMethod{nil},
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HostKeyCallback: ssh.HostKeyCallback(
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func(hostname string, remote net.Addr, key ssh.PublicKey) error {
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return nil
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}),
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}
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}

‎ql/src/experimental/CWE-322/SecureHostKeyCallbackExample.go‎

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package main
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import (
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"golang.org/x/crypto/ssh"
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"io/ioutil"
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)
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func main() {}
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func secureHostKeyCallback() {
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publicKeyBytes, _ := ioutil.ReadFile("allowed_hostkey.pub")
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publicKey, _ := ssh.ParsePublicKey(publicKeyBytes)
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_ = &ssh.ClientConfig{
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User: "username",
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Auth: []ssh.AuthMethod{nil},
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HostKeyCallback: ssh.FixedHostKey(publicKey),
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}
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}

‎ql/src/semmle/go/dataflow/internal/DataFlowUtil.qll‎

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* Gets the dataflow node holding the value of the receiver, if any.
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*/
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abstract ReceiverNode getReceiver();
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/**
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* Gets a value returned by the given function via a return statement or an assignment to a result variable.
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*/
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abstract ResultNode getAResult();
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}
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/** A representation of a function that is declared in the module scope. */
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) {
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func.hasLocationInfo(filepath, startline, startcolumn, endline, endcolumn)
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}
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override ResultNode getAResult() {
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result.getRoot() = getFunction().(DeclaredFunction).getFuncDecl()
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}
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}
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/** A representation of the function that is defined by a function literal. */
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override ReceiverNode getReceiver() { none() }
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override string toString() { result = "function literal" }
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override ResultNode getAResult() { result.getRoot() = getExpr() }
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}
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/** A data flow node that represents a call. */

‎ql/test/experimental/CWE-322/InsecureHostKeyCallback.expected‎

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edges
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| InsecureHostKeyCallbackExample.go:12:4:14:3 | function literal : signature type | InsecureHostKeyCallbackExample.go:11:20:14:4 | type conversion |
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| InsecureHostKeyCallbackExample.go:27:14:30:3 | type conversion : signature type | InsecureHostKeyCallbackExample.go:35:20:35:27 | callback |
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| InsecureHostKeyCallbackExample.go:28:3:30:2 | function literal : signature type | InsecureHostKeyCallbackExample.go:27:14:30:3 | type conversion : signature type |
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| InsecureHostKeyCallbackExample.go:41:3:43:2 | function literal : signature type | InsecureHostKeyCallbackExample.go:48:20:48:48 | type conversion |
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| InsecureHostKeyCallbackExample.go:52:39:52:46 | definition of callback : HostKeyCallback | InsecureHostKeyCallbackExample.go:56:20:56:27 | callback |
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| InsecureHostKeyCallbackExample.go:52:39:52:46 | definition of callback : signature type | InsecureHostKeyCallbackExample.go:56:20:56:27 | callback |
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| InsecureHostKeyCallbackExample.go:63:22:66:3 | type conversion : signature type | InsecureHostKeyCallbackExample.go:68:35:68:50 | insecureCallback : signature type |
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| InsecureHostKeyCallbackExample.go:64:3:66:2 | function literal : signature type | InsecureHostKeyCallbackExample.go:63:22:66:3 | type conversion : signature type |
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| InsecureHostKeyCallbackExample.go:68:35:68:50 | insecureCallback : signature type | InsecureHostKeyCallbackExample.go:52:39:52:46 | definition of callback : signature type |
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| InsecureHostKeyCallbackExample.go:79:35:79:61 | call to InsecureIgnoreHostKey : HostKeyCallback | InsecureHostKeyCallbackExample.go:52:39:52:46 | definition of callback : HostKeyCallback |
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nodes
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| InsecureHostKeyCallbackExample.go:11:20:14:4 | type conversion | semmle.label | type conversion |
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| InsecureHostKeyCallbackExample.go:12:4:14:3 | function literal : signature type | semmle.label | function literal : signature type |
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| InsecureHostKeyCallbackExample.go:22:20:22:46 | call to InsecureIgnoreHostKey | semmle.label | call to InsecureIgnoreHostKey |
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| InsecureHostKeyCallbackExample.go:27:14:30:3 | type conversion : signature type | semmle.label | type conversion : signature type |
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| InsecureHostKeyCallbackExample.go:28:3:30:2 | function literal : signature type | semmle.label | function literal : signature type |
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| InsecureHostKeyCallbackExample.go:35:20:35:27 | callback | semmle.label | callback |
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| InsecureHostKeyCallbackExample.go:41:3:43:2 | function literal : signature type | semmle.label | function literal : signature type |
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| InsecureHostKeyCallbackExample.go:48:20:48:48 | type conversion | semmle.label | type conversion |
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| InsecureHostKeyCallbackExample.go:52:39:52:46 | definition of callback : HostKeyCallback | semmle.label | definition of callback : HostKeyCallback |
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| InsecureHostKeyCallbackExample.go:52:39:52:46 | definition of callback : signature type | semmle.label | definition of callback : signature type |
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| InsecureHostKeyCallbackExample.go:56:20:56:27 | callback | semmle.label | callback |
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| InsecureHostKeyCallbackExample.go:63:22:66:3 | type conversion : signature type | semmle.label | type conversion : signature type |
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| InsecureHostKeyCallbackExample.go:64:3:66:2 | function literal : signature type | semmle.label | function literal : signature type |
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| InsecureHostKeyCallbackExample.go:68:35:68:50 | insecureCallback : signature type | semmle.label | insecureCallback : signature type |
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| InsecureHostKeyCallbackExample.go:79:35:79:61 | call to InsecureIgnoreHostKey : HostKeyCallback | semmle.label | call to InsecureIgnoreHostKey : HostKeyCallback |
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#select
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| InsecureHostKeyCallbackExample.go:11:20:14:4 | type conversion | InsecureHostKeyCallbackExample.go:12:4:14:3 | function literal : signature type | InsecureHostKeyCallbackExample.go:11:20:14:4 | type conversion | Configuring SSH ClientConfig with insecure HostKeyCallback implementation from $@. | InsecureHostKeyCallbackExample.go:12:4:14:3 | function literal | this source |
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| InsecureHostKeyCallbackExample.go:22:20:22:46 | call to InsecureIgnoreHostKey | InsecureHostKeyCallbackExample.go:22:20:22:46 | call to InsecureIgnoreHostKey | InsecureHostKeyCallbackExample.go:22:20:22:46 | call to InsecureIgnoreHostKey | Configuring SSH ClientConfig with insecure HostKeyCallback implementation from $@. | InsecureHostKeyCallbackExample.go:22:20:22:46 | call to InsecureIgnoreHostKey | this source |
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| InsecureHostKeyCallbackExample.go:35:20:35:27 | callback | InsecureHostKeyCallbackExample.go:28:3:30:2 | function literal : signature type | InsecureHostKeyCallbackExample.go:35:20:35:27 | callback | Configuring SSH ClientConfig with insecure HostKeyCallback implementation from $@. | InsecureHostKeyCallbackExample.go:28:3:30:2 | function literal | this source |
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| InsecureHostKeyCallbackExample.go:48:20:48:48 | type conversion | InsecureHostKeyCallbackExample.go:41:3:43:2 | function literal : signature type | InsecureHostKeyCallbackExample.go:48:20:48:48 | type conversion | Configuring SSH ClientConfig with insecure HostKeyCallback implementation from $@. | InsecureHostKeyCallbackExample.go:41:3:43:2 | function literal | this source |
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| InsecureHostKeyCallbackExample.go:56:20:56:27 | callback | InsecureHostKeyCallbackExample.go:64:3:66:2 | function literal : signature type | InsecureHostKeyCallbackExample.go:56:20:56:27 | callback | Configuring SSH ClientConfig with insecure HostKeyCallback implementation from $@. | InsecureHostKeyCallbackExample.go:64:3:66:2 | function literal | this source |
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| InsecureHostKeyCallbackExample.go:56:20:56:27 | callback | InsecureHostKeyCallbackExample.go:79:35:79:61 | call to InsecureIgnoreHostKey : HostKeyCallback | InsecureHostKeyCallbackExample.go:56:20:56:27 | callback | Configuring SSH ClientConfig with insecure HostKeyCallback implementation from $@. | InsecureHostKeyCallbackExample.go:79:35:79:61 | call to InsecureIgnoreHostKey | this source |

‎ql/test/experimental/CWE-322/InsecureHostKeyCallback.qlref‎

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experimental/CWE-322/InsecureHostKeyCallback.ql

‎ql/test/experimental/CWE-322/InsecureHostKeyCallbackExample.go‎

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package main
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import "net"
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import "fmt"
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import "golang.org/x/crypto/ssh"
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func insecureSSHClientConfig() {
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_ = &ssh.ClientConfig{
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User: "user",
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Auth: []ssh.AuthMethod{nil},
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HostKeyCallback: ssh.HostKeyCallback(
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func(hostname string, remote net.Addr, key ssh.PublicKey) error {
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return nil
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}),
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}
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}
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func insecureSSHClientConfigAlt() {
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_ = &ssh.ClientConfig{
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User: "user",
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Auth: []ssh.AuthMethod{nil},
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HostKeyCallback: ssh.InsecureIgnoreHostKey(),
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}
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}
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func insecureSSHClientConfigLocalFlow() {
27+
callback := ssh.HostKeyCallback(
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func(hostname string, remote net.Addr, key ssh.PublicKey) error {
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return nil
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})
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_ = &ssh.ClientConfig{
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User: "user",
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Auth: []ssh.AuthMethod{nil},
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HostKeyCallback: callback,
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}
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}
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func insecureSSHClientConfigLocalFlowAlt() {
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callback :=
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func(hostname string, remote net.Addr, key ssh.PublicKey) error {
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return nil
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};
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_ = &ssh.ClientConfig{
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User: "user",
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Auth: []ssh.AuthMethod{nil},
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HostKeyCallback: ssh.HostKeyCallback(callback),
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}
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}
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func potentialInsecureSSHClientConfig(callback ssh.HostKeyCallback) {
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_ = &ssh.ClientConfig{
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User: "user",
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Auth: []ssh.AuthMethod{nil},
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HostKeyCallback: callback,
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}
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}
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func main() {
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fmt.Printf("Hello insecure SSH client config!\n")
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insecureCallback := ssh.HostKeyCallback(
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func(hostname string, remote net.Addr, key ssh.PublicKey) error {
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return nil
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})
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potentialInsecureSSHClientConfig(insecureCallback)
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potentiallySecureCallback := ssh.HostKeyCallback(
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func(hostname string, remote net.Addr, key ssh.PublicKey) error {
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if hostname == "localhost" {
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return nil
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}
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return fmt.Errorf("ssh: Unexpected host for key")
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})
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potentialInsecureSSHClientConfig(potentiallySecureCallback)
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potentialInsecureSSHClientConfig(ssh.InsecureIgnoreHostKey())
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}

‎ql/test/experimental/CWE-322/go.mod‎

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module custom-queries-go-tests/insecure-ssh-client-config
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go 1.14
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require (
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github.com/github/depstubber v0.0.0-20200618063247-cc37722ad494 // indirect
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golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9
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)

‎ql/test/experimental/CWE-322/vendor/golang.org/LICENSE‎

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