Windows agents connected to Jenkins by SSH hang when cloning an SSH repo from github.com

src/main/java/org/jenkinsci/plugins/gitclient/CliGitAPIImpl.java

@@ -2582,7 +2582,11 @@
             exe = userGitExe + ".exe";
         }
 
-        String[] pathDirs = System.getenv("PATH").split(File.pathSeparator);
+        String path = getEnvVar("PATH");
+        if (path == null) {
+            path = "";
+        }
+        String[] pathDirs = path.split(File.pathSeparator);
 
         for (String pathDir : pathDirs) {
             File exeFile = new File(pathDir, exe);
@@ -2603,8 +2607,13 @@
         return null;
     }
 
+    /* Package protected for testing */
+    String getEnvVar(String envVar) {
+        return System.getenv(envVar);
+    }
+
     private File getFileFromEnv(String envVar, String suffix) {
-        String envValue = System.getenv(envVar);
+        String envValue = getEnvVar(envVar);
         if (envValue == null) {
             return null;
         }
@@ -2689,6 +2698,15 @@
             }
         }
 
+        // Check the system PATH last, the ssh of the git installation is preferred
+        String sshPath = getPathToExe("ssh");
+        if (sshPath != null) {
+            sshexe = new File(sshPath);
+            if (sshexe.exists()) {
+                return sshexe;
+            }
+        }
+
         throw new RuntimeException(
                 "ssh executable not found. The git plugin only supports official git client https://git-scm.com/download/win");
     }

src/test/java/org/jenkinsci/plugins/gitclient/CliGitAPISshExecutableTest.java

@@ -0,0 +1,125 @@
+package org.jenkinsci.plugins.gitclient;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.jvnet.hudson.test.Issue;
+
+/**
+ * Tests the order in which {@link CliGitAPIImpl#getSSHExecutable()} searches for ssh.
+ * The ssh of the git installation must be preferred over an ssh found on the system PATH.
+ *
+ * @author <a href="mailto:akash.manna.mymail@gmail.com">Akash Manna</a>
+ */
+class CliGitAPISshExecutableTest {
+
+    @TempDir
+    private File tempDir;
+
+    private CliGitAPIImpl gitClientWithEnv(String gitExe, Map<String, String> environmentVariables) {
+        return new CliGitAPIImpl(gitExe, tempDir, null, null) {
+            @Override
+            String getEnvVar(String envVar) {
+                return environmentVariables.get(envVar);
+            }
+        };
+    }
+
+    /* Paths are joined with a backslash, so on Unix the file name contains backslashes */
+    private File createExecutable(File executable) throws IOException {
+        File parent = executable.getParentFile();
+        if (parent != null) {
+            parent.mkdirs();
+        }
+        assertTrue(executable.createNewFile(), "Could not create " + executable);
+        return executable;
+    }
+
+    private File pathDirectoryWithSsh() throws IOException {
+        File pathDir = new File(tempDir, "path-dir");
+        pathDir.mkdirs();
+        createExecutable(new File(pathDir, "ssh.exe"));
+        return pathDir;
+    }
+
+    @Test
+    @Issue("JENKINS-1715")
+    void sshOfGitInstallationPreferredOverSshOnPath() throws Exception {
+        File programFiles = new File(tempDir, "Program Files");
+        File gitSsh = createExecutable(new File(programFiles + "\\Git\\bin\\ssh.exe"));
+
+        Map<String, String> env = new HashMap<>();
+        env.put("ProgramFiles", programFiles.getAbsolutePath());
+        env.put("PATH", pathDirectoryWithSsh().getAbsolutePath());
+
+        assertEquals(gitSsh, gitClientWithEnv("git", env).getSSHExecutable());
+    }
+
+    @Test
+    @Issue("JENKINS-1715")
+    void sshOfGitInstallationInUsrBinPreferredOverSshOnPath() throws Exception {
+        File programFiles = new File(tempDir, "Program Files");
+        File gitSsh = createExecutable(new File(programFiles + "\\Git\\usr\\bin\\ssh.exe"));
+
+        Map<String, String> env = new HashMap<>();
+        env.put("ProgramFiles", programFiles.getAbsolutePath());
+        env.put("PATH", pathDirectoryWithSsh().getAbsolutePath());
+
+        assertEquals(gitSsh, gitClientWithEnv("git", env).getSSHExecutable());
+    }
+
+    @Test
+    @Issue("JENKINS-1715")
+    void sshBesideGitExecutablePreferredOverSshOnPath() throws Exception {
+        File gitExe = new File(tempDir, "MinGit\\cmd\\git.exe");
+        File gitSsh = createExecutable(new File(gitExe.getParent() + "\\ssh.exe"));
+
+        Map<String, String> env = new HashMap<>();
+        env.put("PATH", pathDirectoryWithSsh().getAbsolutePath());
+
+        assertEquals(gitSsh, gitClientWithEnv(gitExe.getAbsolutePath(), env).getSSHExecutable());
+    }
+
+    @Test
+    @Issue("JENKINS-72450")
+    void sshOnPathUsedWhenGitInstallationHasNoSsh() throws Exception {
+        File pathDir = pathDirectoryWithSsh();
+
+        Map<String, String> env = new HashMap<>();
+        env.put("PATH", pathDir.getAbsolutePath());
+
+        assertEquals(
+                new File(pathDir, "ssh.exe"),
+                gitClientWithEnv(new File(tempDir, "no-ssh-here\\git.exe").getAbsolutePath(), env)
+                        .getSSHExecutable());
+    }
+
+    @Test
+    @Issue("JENKINS-72450")
+    void gitSshEnvironmentVariablePreferredOverSshOnPath() throws Exception {
+        File gitSshVariable = createExecutable(new File(tempDir, "custom-ssh.exe"));
+
+        Map<String, String> env = new HashMap<>();
+        env.put("GIT_SSH", gitSshVariable.getAbsolutePath());
+        env.put("PATH", pathDirectoryWithSsh().getAbsolutePath());
+
+        assertEquals(gitSshVariable, gitClientWithEnv("git", env).getSSHExecutable());
+    }
+
+    @Test
+    void sshNotFoundReportsUnsupportedGitInstallation() {
+        Map<String, String> env = new HashMap<>();
+        env.put("PATH", new File(tempDir, "empty-dir").getAbsolutePath());
+
+        CliGitAPIImpl git = gitClientWithEnv(new File(tempDir, "no-ssh-here\\git.exe").getAbsolutePath(), env);
+        RuntimeException e = assertThrows(RuntimeException.class, git::getSSHExecutable);
+        assertTrue(e.getMessage().startsWith("ssh executable not found"), e.getMessage());
+    }
+}