CVE-2026-21908: A Use After Free vulnerability was identified in the 802.1X authentication daemon (dot1xd) of Juniper Networks Junos OS and Junos OS Evolved that coul...

Description

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.

Metrics

CVSS 3.1

7.1/10

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

CVSS 4.0

7.5/10

CVSS:4.0/AV:A/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/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:X/R:X/V:X/RE:M/U:Green

EPSS Probability

0.29%

21.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-416

Affected Software

Vendor	Product	Versions	Update
Juniper	Junos	23.2	R2-S1
Juniper	Junos	23.4	R2
Juniper	Junos	24.2	—
Juniper	Junos	24.4	—
Juniper	Junos	25.2	—
Juniper	Junos Os Evolved	23.2	R2-S1
Juniper	Junos Os Evolved	23.4	R2
Juniper	Junos Os Evolved	24.2	—
Juniper	Junos Os Evolved	24.4	—
Juniper	Junos Os Evolved	25.2	—

References

https://kb.juniper.net/JSA106007Vendor Advisory
https://supportportal.juniper.net/JSA106007Vendor Advisory

Timeline

Published: Jan 15, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-21908?

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.

How severe is CVE-2026-21908?

CVE-2026-21908 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.29% probability of exploitation in the next 30 days.

How do I fix CVE-2026-21908?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.