CVE-2025-21594

Remediation / Mitigation Strategy for CVE-2025-21594

Vulnerability Description: Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (pfe) of Juniper Networks Junos OS on MX Series. In a DS-Lite and NAT scenario, when crafted IPv6 traffic is received and the prefix-length is set to 56, the ports assigned to the user are not freed. This leads to exhaustion of available ports, preventing new connections and resulting in Denial of Service (DoS). Affected FPC/PIC require manual restart for recovery.

Severity: High (CVSS Base Score: 8.7)

Known Exploit: Exploitation involves sending crafted IPv6 traffic with a prefix-length of 56 to a Junos OS MX Series device configured for DS-Lite and NAT. This triggers the port exhaustion condition, leading to a DoS.

Affected Versions:

  • from 21.2 before 21.2R3-S8
  • from 21.4 before 21.4R3-S7
  • from 22.1 before 22.1R3-S6
  • from 22.2 before 22.2R3-S4
  • from 22.3 before 22.3R3-S3
  • from 22.4 before 22.4R3-S2
  • from 23.2 before 23.2R2-S1
  • from 23.4 before 23.4R1-S2, 23.4R2

Remediation:

  1. Upgrade Junos OS: The primary remediation is to upgrade Junos OS to a version that includes the fix for CVE-2025-21594. Upgrade to one of the following or a later release:

    • 21.2R3-S8 or later
    • 21.4R3-S7 or later
    • 22.1R3-S6 or later
    • 22.2R3-S4 or later
    • 22.3R3-S3 or later
    • 22.4R3-S2 or later
    • 23.2R2-S1 or later
    • 23.4R1-S2, 23.4R2 or later

    Follow the standard Juniper Networks upgrade procedures and ensure proper testing in a non-production environment before deploying to production.

Mitigation (If immediate patching is not possible):

If an immediate upgrade is not feasible, consider the following mitigations:

  1. Rate Limiting: Implement rate limiting on IPv6 traffic, especially traffic with a prefix-length of 56, to reduce the impact of a potential attack.
  2. Traffic Filtering: Analyze network traffic and filter out any suspicious or malformed IPv6 packets, particularly those with a prefix-length of 56. Implement access control lists (ACLs) to block traffic from known malicious sources.
  3. Monitor NAT Port Usage: Monitor the NAT port usage using the command show services nat source port-block as indicated in the advisory. Look for indications of port exhaustion (e.g., ports used approaching ports total, active blocks with long left times). If port exhaustion is observed, consider temporarily increasing the NAT port pool size and/or restart the affected FPC/PIC to clear the blocked ports, although this is a temporary measure.
  4. DS-Lite Configuration Review: Carefully review DS-Lite configurations and ensure that they are following best practices. Ensure proper input validation and sanitization are in place to prevent malicious traffic from exploiting the vulnerability.
  5. Intrusion Detection/Prevention Systems (IDS/IPS): Configure and enable IDS/IPS systems to detect and potentially block attempts to exploit this vulnerability. Ensure signatures are up to date.
  6. Network Segmentation: Isolate the affected devices within a segmented network to limit the impact of a successful exploit.

Assigner

Date

  • Published Date: 2025-04-09 19:49:41
  • Updated Date: 2025-04-09 20:15:26

More Details

CVE-2025-21594