CVE-2026-21909
Juniper Junos 23.2 … 24.1
Raw 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:GreenSummary
CVE-2026-21909 is a high-severity Missing Release of Memory after Effective Lifetime (CWE-401) vulnerability in Juniper Junos. Its CVSS base score is 7.1 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 15th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SI-2 (Flaw Remediation) and SI-4 (System Monitoring) — see the control section below for these in your framework.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2696
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Direct exploitation of the memory leak vulnerability in rpd via crafted IS-IS packets leads to resource exhaustion and process crash, matching T1499.004 Application or System Exploitation for DoS.
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
Mitigating Controls (NIST 800-53 r5) AI
Directly addresses the memory-leak flaw in rpd IS-IS processing by requiring installation of the listed patched Junos releases.
Boundary-protection rules can restrict or authenticate IS-IS adjacencies, reducing the set of neighbors able to send the malicious update packets.
Continuous monitoring of task memory (as illustrated by the 'show task memory detail' output) detects the progressive TED-INFRA-COOKIE leak before rpd crashes.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly enforce proper memory allocation/deallocation via coding standards, reviews, and tooling.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development can detect unreleased memory, providing partial coverage of the weakness.
Secure development life cycle mandates memory-management practices that reduce missing-release defects.
Application security requirements can specify explicit memory-release rules, partially mitigating the weakness.
Secure system architecture and engineering principles include resource-management guidelines that address memory leaks.
Secure coding standards directly require proper allocation/deallocation, covering most of this weakness.
Capacity management may detect memory exhaustion symptoms but does not prevent the coding flaw.