Medium Memory corruption

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 Jan 15, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: juniper

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.4% (30-day exploitation probability)+4
Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.37%

ahead of 29% of scored CVEs · Oct 15, 2026

Affects

Juniper Networks

Junos and 2 more

CVSS base

6.5

Medium · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

None

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Juniper Networks Junos, Juniper Networks Junos OS, Juniper Networks Junos Os Evolved).
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Juniper Networks	Junos	version 22.4< 22.4version 23.4-r1-s2version 23.4-r1-s1version 23.4-r1version 23.4version 23.2-r2-s4version 23.2-r2-s3 and 21 more version 23.2-r2-s2version 23.2-r2-s1version 23.2-r2version 23.2-r1-s2version 23.2-r1-s1version 23.2-r1version 23.2version 22.4-r3-s6version 22.4-r3-s5version 22.4-r3-s4version 22.4-r3-s3version 22.4-r3-s2version 22.4-r3-s1version 22.4-r3version 22.4-r2-s2version 22.4-r2-s1version 22.4-r2version 22.4-r1-s2version 22.4-r1-s1version 22.4-r1version 22.4-r3-s7	Vulnerable	NIST National Vulnerability Database
Juniper Networks	Junos OS	≥ 23.4 and < 23.4R2< 22.4R3-S8≥ 23.2 and < 23.2R2-S5	Vulnerable	CVE Program (cve.org) e CISA ADP
Juniper Networks	Junos Os Evolved	version 23.2version 23.2-r1version 23.2-r1-s1version 23.2-r1-s2version 23.2-r2version 23.2-r2-s1version 23.2-r2-s2version 23.2-r2-s3 and 21 more version 23.2-r2-s4version 23.4version 23.4-r1version 23.4-r1-s1version 23.4-r1-s2version 22.4-r3-s7version 22.4-r3-s6version 22.4-r3-s5version 22.4-r3-s4version 22.4-r3-s3version 22.4-r3-s2version 22.4-r3-s1version 22.4-r3version 22.4-r2-s2version 22.4-r2-s1version 22.4-r2version 22.4-r1-s2version 22.4-r1-s1version 22.4-r1version 22.4< 22.4	Vulnerable	NIST National Vulnerability Database
Juniper Networks	Junos Os Evolved	< 22.4R3-S8-EVO≥ 23.2 and < 23.2R2-S5-EVO≥ 23.4 and < 23.4R2-EVO	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

Low

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
7.1	CVSS 4.0	High	—	—	sirt@juniper.net via NIST National Vulnerability Database
7.1	CVSS 4.0	High	—	—	juniper via CVE Program (cve.org) e CISA ADP
6.5	CVSS 3.1	Medium	2.8	3.6	sirt@juniper.net via NIST National Vulnerability Database
6.5	CVSS 3.1	Medium	—	—	juniper via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (score shown at the top: sirt@juniper.net)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-416 · Use After Free

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 0.37%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.

web/proxy/WAF logsnetwork IDS/IPSendpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

2026
Affected products added · juniper networks/junos os, juniper networks/junos os evolved
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
CVSS changed · 6.5
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Jan 15, 2026 · juniper

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

2 on the record

kb.juniper.net/JSA106021
Vendor Advisory, vendor-advisory, NIST National Vulnerability Database
supportportal.juniper.net/JSA106021
Vendor Advisory, vendor-advisory, NIST National Vulnerability Database

Elsewhere on this site

Juniper Networks
every CVE for this vendor

Memory corruption
same class

CWE-416
other pages naming this weakness

Related CVEs (same products)

High CVE-2026-102077 Junos OS: MX Series with SPC3: In a source NAT scenario malformed packets will lead to resource leaks and eventually traffic stops 2d
Critical CVE-2026-101982 Junos OS and Junos OS Evolved: A EVPN peer causes an rpd crash or root-level compromise when EVPN-VPWS is used 2d
Critical CVE-2026-101983 Junos OS and Junos OS Evolved: An attacker causes remote code execution when J-Web virtual-domain is configured 2d
High CVE-2026-101981 Junos OS and Junos OS Evolved: An adjacent LDP peer causes routing-engine compromise when LDP is enabled 2d
High CVE-2026-101976 Junos OS and Junos OS Evolved: In a non-4byte-AS scenario a specific BGP update causes an rpd crash 2d
High CVE-2026-101979 Junos OS and Junos OS Evolved: A network attacker causes root-level code execution or denial of service when SNMP and AAA are enabled 2d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-21921 is "Junos OS and Junos OS Evolved: When telemetry collectors are frequently subscribing and unsubscribing to sensors chassisd or rpd will crash", rated Medium. It affects Junos (Juniper Networks); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 6.5 describes technical severity. EPSS 0.37% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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