CVE-2026-21909 - Junos OS Plugin
CVE-2026-21909
A Missing Release of Memory after Effective Lifetime vulnerability in the routing protocol daemon (rpd) Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated attacker controlling an adjacent IS-IS neighbor to send a specific update packet causing a memory leak. Continued receipt and processing of these packets will exhaust all available memory, crashing rpd and creating a Denial of Service (DoS) condition.
Memory usage can be monitored through the use of the 'show task memory detail' command. For example:
user@junos> show task memory detail | match ted-infra
TED-INFRA-COOKIE 25 1072 28 1184 229
user@junos>
show task memory detail | match ted-infra
TED-INFRA-COOKIE 31 1360 34 1472 307
This issue affects:
Junos OS:
* from 23.2 before 23.2R2,
* from 23.4 before 23.4R1-S2, 23.4R2,
* from 24.1 before 24.1R2;
Junos OS Evolved:
* from 23.2 before 23.2R2-EVO,
* from 23.4 before 23.4R1-S2-EVO, 23.4R2-EVO,
* from 24.1 before 24.1R2-EVO.
This issue does not affect Junos OS versions before 23.2R1 or Junos OS Evolved versions before 23.2R1-EVO.
CVE-2026-21909
HIGH
CVSS 7.1
Published 2026-01-15
Updated 2026-01-23
AI Risk Elevated (71/100)
Active Exploit: No strong signal
Published Exploit: No public exploit references
Priority: P3 Priority
Severity Band
HIGH
CVSS Vector
CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:A/V:C/RE:M/U:Green
Affected Components
2
Reference Links
2
AI Risk Engine
Elevated (71/100)
Exploitability
Medium
Active Exploitation
No strong signal
Published Exploit Status
No public exploit references
AI Context
Machine-generated threat intelligence
AI
Updated 10 days ago
AI enriched 10 days ago (2026-04-09 08:01 UTC)
Technical Summary
A Missing Release of Memory after Effective Lifetime vulnerability in the routing protocol daemon (rpd) Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated attacker controlling an adjacent IS-IS neighbor to send a specific update packet causing a memory leak. Continued receipt and processing of these packets will exhaust all available memory, crashing rpd and creating a Denial of Service (DoS) condition. Memory usage can be monitored through the use of the 'show task memory detail' command. For example:…
Potential Impact
Severity is HIGH (CVSS 7.1). Depending on deployment context, affected components may be exposed to unauthorized actions or data integrity risk.
Exploitability Assessment
Exploitability is assessed as Medium based on low-bar exploit prerequisites.
Primary risk drivers: low-bar exploit prerequisites
Mitigation Recommendations
Validate affected product versions, prioritize patching, and monitor references for vendor remediation guidance. If immediate patching is not possible, apply compensating controls and limit exposure of vulnerable surfaces.
Detection & Monitoring
Track authentication anomalies, unexpected file writes, and suspicious plugin API activity around affected components.
Business Impact Lens
Prioritize remediation where affected components process customer data, admin sessions, or Internet-exposed workflows.
