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Fencer Intel
medium 6.5

CVE-2026-21921 json

Junos OS and Junos OS Evolved: When telemetry collectors are frequently subscribing and unsubscribing to sensors chassisd or rpd will crash

published 9mo ago modified 4mo ago also EUVD-2026-2693

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 31%
public exploits
0
none known

Summary

A Use After Free vulnerability in the chassis daemon (chassisd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker authenticated with low privileges to cause a Denial-of-Service (DoS).

When telemetry collectors are frequently subscribing and unsubscribing to sensors continuously over a long period of time, telemetry-capable processes like chassisd, rpd or mib2d will crash and restart, which - depending on the process - can cause a complete outage until the system has recovered.

This issue affects:

Junos OS:

* all versions before 22.4R3-S8, * 23.2 versions before 23.2R2-S5, * 23.4 versions before 23.4R2;

Junos OS Evolved:

* all versions before 22.4R3-S8-EVO, * 23.2 versions before 23.2R2-S5-EVO, * 23.4 versions before 23.4R2-EVO.

Patch / fix

  • Juniper Networks Junos OS 22.4R3-S8, 23.2R2-S5, 23.4R2
  • Juniper Networks Junos OS Evolved 22.4R3-S8-EVO, 23.2R2-S5-EVO, 23.4R2-EVO

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CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
9mo ago

Exploit prediction

0.37% chance of exploitation in the next 30 days, higher than 31% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CNA 4.0 7.1 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/RE:M
CNA 4.0 7.1 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/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:X/RE:M/U:X

Affected products

  • Juniper Networks Junos OS
  • Juniper Networks Junos OS Evolved

Classification

Weakness

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.