High priorityDisclosed

Advisory · CVE-2026-102023

Reachable assertion in Junos OS Evolved firewall stats daemon falls over on an SNMP query

A reachable assertion vulnerability in fwstatsd of Junos OS Evolved lets an authenticated network attacker cause a denial of service via an SNMP firewall-counter MIB query when at least one firewall counter is configured. 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 Evolved
Identifier / CWE
CVE-2026-102023
CWE-617
Action timing
Immediate
ELI5

Explain it like I’m five

Asking the device how many packets its firewall counted can crash the daemon that does the counting.

SIMPLIFIED_ATTACK_PATH03 STEPS
  1. 01Trigger input

    An attacker sends the crafted protocol traffic described for CVE-2026-102023.

  2. 02Weakness trips

    The daemon mishandles the input through the reachable assertion weakness.

  3. 03Impact lands

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

What happened

Juniper disclosed CVE-2026-102023 in its October 2026 security release: a reachable assertion vulnerability (CWE-617) in fwstatsd on Junos OS Evolved. An SNMP firewall-counter MIB query from an authenticated network attacker can deny service when at least one firewall counter is configured.

Juniper’s JSA112250 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 Evolved 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 Evolved while remediation is underway, especially for internet-facing instances.
  4. Review application and server logs for fwstatsd crashes and SNMP timeouts when firewall counters are polled.
  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

Monitoring credentials plus one MIB walk should never be a denial of service. Patch and restrict SNMP sources.