High priorityDisclosed

Advisory · CVE-2026-102027

Buffer size miscalculation in Junos rpd lets an eBGP neighbor crash it via labeled-unicast

An incorrect calculation of buffer size vulnerability in the routing protocol daemon (rpd) of Junos OS and Junos OS Evolved lets a configured eBGP neighbor cause an rpd crash via BGP labeled-unicast UPDATEs when the affected multipath features are enabled. Juniper rates it CVSS 4.0 8.7 (CVSS 3.1 7.5).

Advisory published October 14, 2026Independent summary
Vendor
Juniper Networks
Product
Junos OS
Identifier / CWE
CVE-2026-102027
CWE-131
Action timing
Immediate
ELI5

Explain it like I’m five

The daemon sizes a buffer with the wrong math for multipath routes, and a neighbor's update does the rest.

SIMPLIFIED_ATTACK_PATH03 STEPS
  1. 01Trigger input

    An attacker sends the crafted protocol traffic described for CVE-2026-102027.

  2. 02Weakness trips

    The daemon mishandles the input through the incorrect calculation of buffer size weakness.

  3. 03Impact lands

    The routing or control-plane daemon crashes or misbehaves as described.

What happened

Juniper disclosed CVE-2026-102027 in its October 2026 security release: an incorrect calculation of buffer size (CWE-131) in rpd. A configured eBGP neighbor can crash rpd via BGP labeled-unicast UPDATEs when the affected multipath features are enabled. The vendor record lists affected releases starting with the 24.4 line.

Juniper’s JSA112187 lists the affected service releases and the October 2026 service release thresholds that carry the fix. Match your exact release to the advisory rather than guessing here.

What to do

  1. Inventory every Junos OS deployment, including test, training, and individually managed instances.
  2. Apply the vendor fix or upgrade exactly as directed in the linked vendor bulletin or advisory.
  3. Restrict network access to Junos OS while remediation is underway, especially for internet-facing instances.
  4. Review application and server logs for rpd crashes following labeled-unicast updates on multipath-enabled devices.
  5. Check for accounts, content, or configuration created outside normal change processes, and rotate exposed credentials where access cannot be ruled out.
  6. Verify the deployed version or patch level after remediation.

Management note

Labeled-unicast is core MPLS plumbing. Patch and confirm multipath sessions re-converge cleanly.