CVE-2026-101939 Juniper Networks CVE debrief

Who should care

Network administrators and security teams responsible for managing and securing Junos OS and Junos OS Evolved systems should assess their configurations and take steps to prevent potential denial-of-service attacks.

Why it matters

A denial-of-service vulnerability exists in Juniper Networks Junos OS and Junos OS Evolved when source-based forwarding is used. Network administrators and security teams should assess their configurations and take steps to prevent potential denial-of-service attacks.

• Denial of service to routing daemon
• Potential network instability or downtime
• Need to verify and update Junos OS and Junos OS Evolved configurations
• Possible impact on network availability and reliability

Technical summary

A NULL Pointer Dereference vulnerability in the routing protocol daemon (RPD) of Juniper Networks Junos OS and Junos OS Evolved allows a configured peer sending a BGP UPDATE to cause a denial of service when an import policy with `then source-based-forwarding next-hop next-table <X>` is configured to reference a routing table that does not exist. The vulnerability affects network administrators and security teams, who should assess their configurations and take steps to prevent potential denial-of-service attacks. The issue can be triggered by a BGP UPDATE message and can cause a denial of service to the routing daemon, potentially leading to network instability or downtime.

Defensive priority

Network administrators should prioritize verifying and updating their Junos OS and Junos OS Evolved configurations to prevent potential denial-of-service attacks.

Recommended defensive actions

• Verify and update Junos OS and Junos OS Evolved configurations to prevent potential denial-of-service attacks
• Check for and apply vendor-provided patches or updates
• Monitor network activity for suspicious BGP UPDATE messages
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed

Evidence notes

The CVE record and source item provide details on the vulnerability, including affected versions of Junos OS and Junos OS Evolved. However, the corpus does not provide information on exploitation or specific attack vectors.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.