A Missing Release of Resource after Effective Lifetime vulnerability the xinetd process, responsible for spawning SSH daemon (sshd) instances, of Juniper Networks Junos OS Evolved allows an unauthenticated network-based attacker to cause a Denial of Service (DoS) by blocking SSH access for legitimate users. Continued receipt of these connections will create a sustained Denial of Service (DoS) condition.

The issue is triggered when a high rate of concurrent SSH requests are received and terminated in a specific way, causing xinetd to crash, and leaving defunct sshd processes. Successful exploitation of this vulnerability blocks both SSH access as well as services which rely upon SSH, such as SFTP, and Netconf over SSH.

Once the system is in this state, legitimate users will be unable to SSH to the device until service is manually restored.  See WORKAROUND section below.

Administrators can monitor an increase in defunct sshd processes by utilizing the CLI command:

  > show system processes | match sshd
  root   25219 30901 0 Jul16 ?       00:00:00 [sshd] <defunct>

This issue affects Juniper Networks Junos OS Evolved:

• All versions prior to 21.4R3-S7-EVO
• 22.3-EVO versions prior to 22.3R2-S2-EVO, 22.3R3-S2-EVO;
• 22.4-EVO versions prior to 22.4R3-EVO;
• 23.2-EVO versions prior to 23.2R2-EVO.

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue was seen during production usage.

The following software releases have been updated to resolve this specific issue: Junos OS Evolved 21.4R3-S7-EVO, 22.2R1-EVO, 22.3R2-S2-EVO, 22.3R3-S2-EVO, 22.4R3-EVO, 23.2R2-EVO, 23.4R1-EVO, and all subsequent releases.

This issue is being tracked as 1741624 which is visible on the Customer Support website.

Note: Juniper SIRT's policy is not to evaluate releases which are beyond End of Engineering (EOE) or End of Life (EOL).

Use access lists or firewall filters to limit access to the device via SSH only from trusted hosts.

Service Restoration

SSH service may be restored by restarting the xinetd-external.service via the following shell command:

2024-09-13: Minor formatting change to cvss field.
2024-07-10: Initial Publication

• KB16613: Overview of the Juniper Networks SIRT Quarterly Security Bulletin Publication Process [juniper.net]
• KB16765: In which releases are vulnerabilities fixed? [juniper.net]
• KB16446: Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories [juniper.net]
• Report a Security Vulnerability - How to Contact the Juniper Networks Security Incident Response Team