CVE-2026-21921 | Junos OS and Junos OS Evolved: When telemetry collectors are frequently subscribing and unsubscribing to sensors chassisd or rpd will crash

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.

Published: 2026-01-15 Last update: 2026-01-23 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-21921 is rated Low Risk (32.6/100): CVSS High severity, with low exploitation likelihood (EPSS 0.04%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-21921

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-01-16 — 0.04% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-21921

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.1 4.0 HIGH
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 Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network.
Attack complexity (AC:L)
Exploitation conditions are straightforward and stable.
Attack requirements (AT:N)
No additional preconditions are required beyond normal reachability.
Privileges required (PR:L)
Low privileges are required.
User interaction (UI:N)
No user interaction is required.
Vulnerable system confidentiality impact (VC:N)
No confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:N)
No integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:H)
High availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:N)
No confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:N)
No integrity impact on subsequent systems.
Subsequent system availability impact (SA:L)
Limited availability impact on subsequent systems.
Exploit maturity (threat) (E:X)
Not defined: no reliable threat intelligence; scoring assumes the worst case (equivalent to Attacked).
Confidentiality requirement (CR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Integrity requirement (IR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Availability requirement (AR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Modified attack vector (MAV:X)
Not defined: scoring uses the Base Attack Vector (AV).
Modified attack complexity (MAC:X)
Not defined: scoring uses the Base Attack Complexity (AC).
Modified attack requirements (MAT:X)
Not defined: scoring uses the Base Attack Requirements (AT).
Modified privileges required (MPR:X)
Not defined: scoring uses the Base Privileges Required (PR).
Modified user interaction (MUI:X)
Not defined: scoring uses the Base User Interaction (UI).
Modified vulnerable system confidentiality impact (MVC:X)
Not defined: scoring uses the Base VC metric.
Modified vulnerable system integrity impact (MVI:X)
Not defined: scoring uses the Base VI metric.
Modified vulnerable system availability impact (MVA:X)
Not defined: scoring uses the Base VA metric.
Modified subsequent system confidentiality impact (MSC:X)
Not defined: scoring uses the Base SC metric.
Modified subsequent system integrity impact (MSI:X)
Not defined: scoring uses the Base SI metric.
Modified subsequent system availability impact (MSA:X)
Not defined: scoring uses the Base SA metric.
Safety (supplemental) (S:X)
Not evaluated.
Automatable (supplemental) (AU:Y)
Yes: all four kill-chain steps (reconnaissance, weaponization, delivery, exploitation) can be automated.
Recovery (supplemental) (R:A)
Automatic: services recover on their own after an attack.
Value density (supplemental) (V:X)
Not evaluated.
Vulnerability response effort (supplemental) (RE:M)
Moderate effort (remote update, disable subsystem, simple upgrade with minor service impact).
Provider urgency (supplemental) (U:X)
Not evaluated.
 — — [email protected]
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 3.6 [email protected]

Weakness enumeration for CVE-2026-21921

Affected software / configurations for CVE-2026-21921

Vendor Product Version Raw CPE
juniper junos < 22.4 cpe:2.3:o:juniper:junos:*:*:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:-:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r1:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r1-s1:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r1-s2:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r2:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r2-s1:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r2-s2:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r3:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r3-s1:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r3-s2:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r3-s3:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r3-s4:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r3-s5:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r3-s6:*:*:*:*:*:*
juniper junos 22.4 cpe:2.3:o:juniper:junos:22.4:r3-s7:*:*:*:*:*:*
juniper junos 23.2 cpe:2.3:o:juniper:junos:23.2:-:*:*:*:*:*:*
juniper junos 23.2 cpe:2.3:o:juniper:junos:23.2:r1:*:*:*:*:*:*
juniper junos 23.2 cpe:2.3:o:juniper:junos:23.2:r1-s1:*:*:*:*:*:*
juniper junos 23.2 cpe:2.3:o:juniper:junos:23.2:r1-s2:*:*:*:*:*:*
juniper junos 23.2 cpe:2.3:o:juniper:junos:23.2:r2:*:*:*:*:*:*
juniper junos 23.2 cpe:2.3:o:juniper:junos:23.2:r2-s1:*:*:*:*:*:*
juniper junos 23.2 cpe:2.3:o:juniper:junos:23.2:r2-s2:*:*:*:*:*:*
juniper junos 23.2 cpe:2.3:o:juniper:junos:23.2:r2-s3:*:*:*:*:*:*
juniper junos 23.2 cpe:2.3:o:juniper:junos:23.2:r2-s4:*:*:*:*:*:*
juniper junos 23.4 cpe:2.3:o:juniper:junos:23.4:-:*:*:*:*:*:*
juniper junos 23.4 cpe:2.3:o:juniper:junos:23.4:r1:*:*:*:*:*:*
juniper junos 23.4 cpe:2.3:o:juniper:junos:23.4:r1-s1:*:*:*:*:*:*
juniper junos 23.4 cpe:2.3:o:juniper:junos:23.4:r1-s2:*:*:*:*:*:*
juniper junos_os_evolved < 22.4 cpe:2.3:o:juniper:junos_os_evolved:*:*:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:-:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r1:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r1-s1:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r1-s2:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r2:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r2-s1:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r2-s2:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r3:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r3-s1:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r3-s2:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r3-s3:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r3-s4:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r3-s5:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r3-s6:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r3-s7:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:-:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r1:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r1-s1:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r1-s2:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r2:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r2-s1:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r2-s2:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r2-s3:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r2-s4:*:*:*:*:*:*
juniper junos_os_evolved 23.4 cpe:2.3:o:juniper:junos_os_evolved:23.4:-:*:*:*:*:*:*
juniper junos_os_evolved 23.4 cpe:2.3:o:juniper:junos_os_evolved:23.4:r1:*:*:*:*:*:*
juniper junos_os_evolved 23.4 cpe:2.3:o:juniper:junos_os_evolved:23.4:r1-s1:*:*:*:*:*:*
juniper junos_os_evolved 23.4 cpe:2.3:o:juniper:junos_os_evolved:23.4:r1-s2:*:*:*:*:*:*

References for CVE-2026-21921

cvelogic Threat Intelligence