Jenkins 2.213 and earlier, LTS 2.204.1 and earlier includes support for the Inbound TCP Agent Protocol/3 for communication between controller and agents. While this protocol has been deprecated in 2018 and was recently removed from Jenkins in 2.214, it could still easily be enabled in Jenkins LTS 2.204.1, 2.213, and older.
This protocol incorrectly reuses encryption parameters which allow an unauthenticated remote attacker to determine the connection secret. This secret can then be used to connect attacker-controlled Jenkins agents to the Jenkins controller.
Jenkins 2.204.2 no longer allows for the use of Inbound TCP Agent Protocol/3 by default. The system property jenkins.slaves.JnlpSlaveAgentProtocol3.ALLOW_UNSAFE
can be set to true
to allow enabling the Inbound TCP Agent Protocol/3 in Jenkins 2.204.2, but doing so is strongly discouraged.
Inbound TCP Agent Protocol/3 was removed completely from Jenkins 2.214 and will not be part of Jenkins LTS after the end of the 2.204.x line.
www.openwall.com/lists/oss-security/2020/01/29/1
access.redhat.com/errata/RHBA-2020:0402
access.redhat.com/errata/RHBA-2020:0675
access.redhat.com/errata/RHSA-2020:0681
access.redhat.com/errata/RHSA-2020:0683
github.com/jenkinsci/jenkins
github.com/jenkinsci/jenkins/commit/5054bc6e12e1022993d719f66e289ab1d22ae854
jenkins.io/security/advisory/2020-01-29/#SECURITY-1682
nvd.nist.gov/vuln/detail/CVE-2020-2099