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  1. Jenkins
  2. JENKINS-31549

sshcredentials via trilead-ssh2 Cannot Connect to Servers Requiring Strong MACs

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Details

    • Bug
    • Status: Resolved (View Workflow)
    • Minor
    • Resolution: Fixed
    • ssh-slaves-plugin
    • None
    • Jenkins 1.638; SSH Credentials Plugin 1.11; CentOS 7.1.1503; openjdk 1.8

    Description

      master cannot connect to slave

      /var/log/secure on slave reports
      sshd[1978]: fatal: no matching mac found: client hmac-sha1-96,hmac-sha1,hmac-md5-96,hmac-md5 server hmac-sha2-512,hmac-sha2-256,hmac-ripemd160

      master reports

      Key exchange was not finished, connection is closed.
ERROR: Unexpected error in launching a slave. This is probably a bug in Jenkins.
java.lang.IllegalStateException: Connection is not established!
	at com.trilead.ssh2.Connection.getRemainingAuthMethods(Connection.java:1030)
	at com.cloudbees.jenkins.plugins.sshcredentials.impl.TrileadSSHPublicKeyAuthenticator.getRemainingAuthMethods(TrileadSSHPublicKeyAuthenticator.java:88)
	at com.cloudbees.jenkins.plugins.sshcredentials.impl.TrileadSSHPublicKeyAuthenticator.canAuthenticate(TrileadSSHPublicKeyAuthenticator.java:80)
	at com.cloudbees.jenkins.plugins.sshcredentials.SSHAuthenticator.newInstance(SSHAuthenticator.java:207)
	at com.cloudbees.jenkins.plugins.sshcredentials.SSHAuthenticator.newInstance(SSHAuthenticator.java:169)
	at hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:1212)
	at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:711)
	at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:706)
	at java.util.concurrent.FutureTask.run(FutureTask.java:262)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)

      This is related to JENKINS-26379 but the comments in that ticket only hint at the issue which, to writ, is:
      https://github.com/jenkinsci/trilead-ssh2/blob/master/src/com/trilead/ssh2/crypto/digest/MAC.java

      com.trilead.ssh2.crypto.digest.MAC
      	public final static String[] getMacList()
	{
		/* Higher Priority First */

		return new String[] { "hmac-sha1-96", "hmac-sha1", "hmac-md5-96", "hmac-md5" };
	}

      See https://stribika.github.io/2015/01/04/secure-secure-shell.html

      Here are the available MAC choices:

      hmac-md5
      hmac-md5-96
      hmac-ripemd160
      hmac-sha1
      hmac-sha1-96
      hmac-sha2-256
      hmac-sha2-512
      umac-64
      umac-128
      hmac-md5-etm@openssh.com
      hmac-md5-96-etm@openssh.com
      hmac-ripemd160-etm@openssh.com
      hmac-sha1-etm@openssh.com
      hmac-sha1-96-etm@openssh.com
      hmac-sha2-256-etm@openssh.com
      hmac-sha2-512-etm@openssh.com
      umac-64-etm@openssh.com
      umac-128-etm@openssh.com
      The selection considerations:

      Security of the hash algorithm: No MD5 and SHA1. Yes, I know that HMAC-SHA1 does not need collision resistance but why wait? Disable weak crypto today.
      Encrypt-then-MAC: I am not aware of a security proof for CTR-and-HMAC but I also don't think CTR decryption can fail. Since there are no downgrade attacks, you can add them to the end of the list. You can also do this on a host by host basis so you know which ones are less safe.
      Tag size: At least 128 bits. This eliminates umac-64-etm.
      Key size: At least 128 bits. This doesn't eliminate anything at this point.
      Recommended /etc/ssh/sshd_config snippet:

      MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-ripemd160-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160,umac-128@openssh.com

      Attachments

        Issue Links

          is duplicated by

          Improvement - An improvement or enhancement to an existing feature or task. JENKINS-33021 trilead ssh MAC and key exchange algorithms severely outdated

          • Critical - Crashes, loss of data, severe memory leak.
          • Resolved
          is related to

          Bug - A problem which impairs or prevents the functions of the product. JENKINS-26379 Jenkins - ssh connection exception

          • Major - Major loss of function.
          • Resolved

          Activity

            Ascending order - Click to sort in descending order
            sheatomsin Shea Tomsin added a comment -

            I checked:

            project = JENKINS AND status in (Open, "In Progress", Reopened) AND component = 'ssh-credentials-plugin' and (text ~ mac or text ~ auth)

            before I created this ticket

            sheatomsin Shea Tomsin added a comment - I checked: project = JENKINS AND status in (Open, "In Progress", Reopened) AND component = 'ssh-credentials-plugin' and (text ~ mac or text ~ auth) before I created this ticket
            stephenconnolly Stephen Connolly added a comment -

            Not an issue with ssh-credentials-api-plugin but rather an issue in ssh-slaves-plugin

            stephenconnolly Stephen Connolly added a comment - Not an issue with ssh-credentials-api-plugin but rather an issue in ssh-slaves-plugin
            scm_issue_link SCM/JIRA link daemon added a comment -

            Code changed in jenkins
            User: Michael Clarke
            Path:
            core/pom.xml
            http://jenkins-ci.org/commit/jenkins/b17d0763709be35d39f16d6af7afaf765ac6cf92
            Log:
            Bump Trilead version to receive a number of security enhancements
            JENKINS-41606JENKINS-33021JENKINS-26379JENKINS-31549

            scm_issue_link SCM/JIRA link daemon added a comment - Code changed in jenkins User: Michael Clarke Path: core/pom.xml http://jenkins-ci.org/commit/jenkins/b17d0763709be35d39f16d6af7afaf765ac6cf92 Log: Bump Trilead version to receive a number of security enhancements JENKINS-41606 JENKINS-33021 JENKINS-26379 JENKINS-31549
            oleg_nenashev Oleg Nenashev added a comment -

            The fix has been integrated towards 2.58. It is not a backporting candidate

            oleg_nenashev Oleg Nenashev added a comment - The fix has been integrated towards 2.58. It is not a backporting candidate

            People

              mc1arke Michael Clarke
              sheatomsin Shea Tomsin
              Votes:
              5 Vote for this issue
              Watchers:
              11 Start watching this issue

              Dates

                Created:
                Updated:
                Resolved: