Junos
CVE-2026-21908
HIGH
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessAuthenticate to network as adjacent user
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ExploitTrigger port flap event
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ExecutionCause CoA processing with freed pointer
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ImpactCrash dot1xd daemon or execute arbitrary code as root
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2021 - Vulnerable and Outdated Components
ASVS 5.0
V15 - Secure Coding and Architecture Memory lifecycle management
MITRE ATT&CK
2 techniques across 2 tactics: Execution, Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Authenticated network-adjacent access to Juniper Junos OS or Junos OS Evolved device; 802.1X authentication daemon (dot1xd) enabled; ability to perform port bounce operations on managed network interface; exploitation requires timing control over port state changes during CoA message processing. |
| Impact | CVSS 7.1 (HIGH). Attack vector: Adjacent Network. Complexity: High. Privileges required: Low. User interaction: None. Exploitation requires authentication. Exploitable via remote/network. |
| Exploit ScenarioDerived | A remote attacker (requires authentication) could exploit this vulnerability to an authenticated, network-adjacent attacker flapping a port to crash the dot1xd. |
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Alert meAnalysisAIv1 – Mar 12, 2026
Juniper Junos OS and Junos OS Evolved contain a use-after-free vulnerability in the 802.1X authentication daemon that allows authenticated, network-adjacent attackers to crash the process or achieve arbitrary code execution as root by triggering specific port state changes. Exploitation requires precise timing of a change-of-authorization event during port transitions, making reliable exploitation difficult but possible. Systems with 802.1X port-based network access control enabled are affected, and no patch is currently available.
Earlier versions of this analysis (1)
A Use After Free vulnerability was identified in the 802.1X authentication daemon (dot1xd) of Juniper Networks Junos OS and Junos OS Evolved that could allow an authenticated, network-adjacent attacker flapping a port to crash the dot1xd process, leading to a Denial of Service (DoS), or potentially execute arbitrary code within the context of the process running as root. [CVSS 7.1 HIGH]
RemediationAI
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Affects your stack
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Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
Classified as CWE-416 (Use After Free). Affects Junos. A Use After Free vulnerability was identified in the 802.1X authentication daemon (dot1xd) of Juniper Networks Junos OS and Junos OS Evolved that could allow an authenticated, network-adjacent attacker flapping a port to crash the dot1xd process, leading to a Denial of Service (DoS), or potentially execute arbitrary code within the context of the process running as root.
The issue is specific to the processing of a change in authorization (CoA) when a port bounce occurs. A pointer is freed but
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:A/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
DescriptionCVE.org
A Use After Free vulnerability was identified in the 802.1X authentication daemon (dot1xd) of Juniper Networks Junos OS and Junos OS Evolved that could allow an authenticated, network-adjacent attacker flapping a port to crash the dot1xd process, leading to a Denial of Service (DoS), or potentially execute arbitrary code within the context of the process running as root.
The issue is specific to the processing of a change in authorization (CoA) when a port bounce occurs. A pointer is freed but was then referenced later in the same code path. Successful exploitation is outside the attacker's direct control due to the specific timing of the two events required to execute the vulnerable code path.
This issue affects systems with 802.1X authentication port-based network access control (PNAC) enabled. This issue affects:
Junos OS:
- from 23.2R2-S1 before 23.2R2-S5,
- from 23.4R2 before 23.4R2-S6,
- from 24.2 before 24.2R2-S3,
- from 24.4 before 24.4R2-S1,
- from 25.2 before 25.2R1-S2, 25.2R2;
Junos OS Evolved:
- from 23.2R2-S1 before 23.2R2-S5-EVO,
- from 23.4R2 before 23.4R2-S6-EVO,
- from 24.2 before 24.2R2-S3-EVO,
- from 24.4 before 24.4R2-S1-EVO,
- from 25.2 before 25.2R1-S2-EVO, 25.2R2-EVO.
Executive ViewAI
Organizations using A Use After Free vulnerability face moderate risk from CVE-2026-21908, a use-after-free vulnerability rated CVSS 7.1. Exploitation could compromise the security of affected deployments. Organizations should apply vendor updates when available and consider compensating controls in the interim.
Apply vendor patch. If immediate patching is not feasible: (1) Enable ASLR and DEP where available; (2) Implement network segmentation; (3) Monitor for exploitation indicators.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Use-after-free vulnerabilities occur when a program continues to access memory through a pointer after that memory has been deallocated.
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
Affected Products (CPE)CVE.org
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A security vulnerability in An Improper (CVSS 6.7) that allows a local attacker with high privileges. Risk factors: acti
A PHP External Variable Modification vulnerability in J-Web of Juniper Networks Junos OS on EX Series and SRX Series all
jsdm/ajax/port.php in J-Web in Juniper Junos before 10.4R13, 11.4 before 11.4R7, 12.1 before 12.1R5, 12.2 before 12.2R3,
Juniper Junos 11.4 before R11, 12.1 before R9, 12.1X44 before D30, 12.1X45 before D20, 12.1X46 before D15, 12.1X47 befor
NFX Series devices using Juniper Networks Junos OS are susceptible to a local command execution vulnerability thereby al
NFX Series devices using Juniper Networks Junos OS are susceptible to a local code execution vulnerability thereby allow
Insufficient validation of environment variables in the telnet client supplied in Junos OS can lead to stack-based buffe
An Out-of-Bounds Write vulnerability in the H.323 ALG of Juniper Networks Junos OS allows an unauthenticated, network-ba
On QFX10000 Series devices using Juniper Networks Junos OS when configured as transit IP/MPLS penultimate hop popping (P
A Missing Release of Memory after Effective Lifetime vulnerability in the kernel of Juniper Networks Junos OS allows an
GitHub PoC
Exploit-DB