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JunosOperating system · Juniper

CVE-2026-21908

HIGH · 7.1 CVSS v3.1 Published 2026-01-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
73/100
Remediation priority · Elevated
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Use After Free vulnerability in Juniper's 802.1X authentication daemon (dot1xd) where a pointer is freed but still referenced during Change of Authorization (CoA) processing when a port bounce occurs. An authenticated network-adjacent attacker can trigger port flapping to crash the dot1xd process (DoS) or potentially achieve arbitrary code execution as root.

MitigationDisable 802.1X (PNAC) on all ports if not required, or apply Juniper's vendor patches (upgrade to fixed versions: 23.2R2-S5, 23.4R2-S6, 24.2R2-S3, 24.4R2-S1, 25.2R1-S2, or 25.2R2 and later).

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
JunosOperating system
Affected:= 23.2= 23.4= 24.2= 24.4= 25.2
Junos Os EvolvedOperating system
Affected:= 23.2= 23.4= 24.2= 24.4= 25.2

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
High
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:A/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check Junos version
    Run `show version` on the device CLI to obtain the installed Junos version.
    Affected if The version matches 23.2, 23.4, 24.2, 24.4, or 25.2 base releases before patches are applied.
  2. Confirm 802.1X is enabled
    Run `show dot1x summary` or check the configuration with `show configuration protocols dot1x` to see if 802.1X (PNAC) is configured on any interfaces.
    Affected if 802.1X authentication is enabled on one or more interfaces (the dot1xd daemon is active).
  3. Verify dot1xd process is running
    Run `show system processes dot1xd` or `request system process daemon dot1xd status` to confirm the dot1xd daemon is running.
    Affected if The dot1xd process is active and running on the device.
  4. Check for Change of Authorization (CoA) configuration
    Review the RADIUS server configuration with `show configuration access` to see if CoA is configured, as the vulnerability triggers during CoA processing.
    Affected if CoA messages are accepted from a RADIUS server (this is the condition where the UAF triggers during port bounce).

The device is affected if it runs a vulnerable Junos base version (23.2/23.4/24.2/24.4/25.2), has 802.1X enabled on any ports, and the dot1xd daemon is running to process authentication requests.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Disable 802.1X (PNAC) on all ports if not required, or apply Juniper's vendor patches (upgrade to fixed versions: 23.2R2-S5, 23.4R2-S6, 24.2R2-S3, 24.4R2-S1, 25.2R1-S2, or 25.2R2 and later).

Recommended fix High confidence

Upgrade to the fixed S-release or R2-release for your version branch (e.g., 23.2R2-S5, 23.4R2-S6, 24.2R2-S3, 24.4R2-S1, or 25.2R2)

  1. 1. Identify the currently running Junos OS or Junos OS Evolved version using 'show version'
  2. 2. Determine which version branch you're on (23.2, 23.4, 24.2, 24.4, or 25.2)
  3. 3. If running an affected version, plan an upgrade to the appropriate fixed release for your branch
  4. 4. For Junos OS 23.2.x: upgrade to 23.2R2-S5 or later
  5. 5. For Junos OS 23.4.x: upgrade to 23.4R2-S6 or later
  6. 6. For Junos OS 24.2.x: upgrade to 24.2R2-S3 or later
  7. 7. For Junos OS 24.4.x: upgrade to 24.4R2-S1 or later
  8. 8. For Junos OS 25.2.x: upgrade to 25.2R1-S2 or 25.2R2 or later
Caveat Standard Junos upgrade precautions apply - test in lab first, schedule maintenance window, backup configuration

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-21908 in production — separate from our analysis above.

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