Medium Memory corruption exploit reference

CVE-2026-21901 — Junos OS and Junos OS Evolved: Configuration of a specific SSH option results in mgd crash

A NULL Pointer Dereference vulnerability in the management daemon (mgd) of Juniper Networks Junos OS and Junos OS Evolved allows a local, high-privileged attacker setting or deactivating a specific SSH configuration parameter to create a Denial of Service (DoS). A local high-privileged user configuring or deactivating a specific 'system services ssh' configuration parameter can exploit a null pointer dereference in one of the functions used by SSH. The function attempts to dereference a null pointer when accessing certain configuration data, resulting in an mgd process crash and restart. Continued execution of these configuration commands will create a sustained Denial of Service (DoS) condition. This issue affects: Junos OS: * from 22.3 before 22.3R3-S5; * from 22.4 before 22.4R3-S10; * from 23.2 before 23.2R2-S7; * from 23.4 before 23.4R2-S8. This issue does not affect Junos OS before 22.3R1. Junos OS Evolved: * from 22.3R1-EVO before 23.2R2-S7-EVO; * from 23.4 before 23.4R2-S8-EVO. This issue does not affect Junos OS Evolved before 22.3R1-EVO.

Published Jul 9, 2026 · Updated Oct 15, 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

Technical severity (medium)+3
CISA SSVC: exploitation "poc"+5

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

—

No EPSS score.

Affects

Juniper Networks

Junos and 2 more

CVSS base

4.4

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

Proof of concept

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.

Documented mitigation — github.com (NIST National Vulnerability Database)

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).
Apply the documented mitigations until a definitive fix is available.
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 22.3version 22.3-r1-s1version 22.3-r1-s2version 22.3-r2version 22.3-r2-s1version 22.3-r2-s2version 22.3-r3version 22.3-r3-s1 and 43 more version 22.3-r3-s2version 22.3-r3-s3version 22.3-r3-s4version 22.4version 22.4-r1version 22.4-r1-s1version 22.4-r1-s2version 22.4-r2version 22.4-r2-s1version 22.4-r2-s2version 22.4-r3version 22.4-r3-s1version 22.4-r3-s2version 22.4-r3-s3version 22.4-r3-s4version 22.4-r3-s5version 22.4-r3-s6version 22.4-r3-s7version 22.4-r3-s8version 22.4-r3-s9version 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-s3version 23.2-r2-s4version 23.2-r2-s5version 23.2-r2-s6version 23.4version 23.4-r1version 23.4-r1-s1version 23.4-r1-s2version 23.4-r2version 23.4-r2-s1version 23.4-r2-s2version 23.4-r2-s3version 23.4-r2-s4version 23.4-r2-s5version 23.4-r2-s6version 23.4-r2-s7	Vulnerable	NIST National Vulnerability Database
Juniper Networks	Junos OS	≥ 22.3 and < 22.3R3-S5≥ 22.4 and < 22.4R3-S10≥ 23.2 and < 23.2R2-S7≥ 23.4 and < 23.4R2-S8	Vulnerable	CVE Program (cve.org) e CISA ADP
Juniper Networks	Junos Os Evolved	version 22.3-r1version 22.3-r1-s1version 22.3-r1-s2version 22.3-r2version 22.3-r2-s1version 22.3-r2-s2version 22.3-r3version 22.3-r3-s1 and 45 more version 22.3-r3-s2version 22.3-r3-s3version 22.4version 22.4-r1version 22.4-r1-s1version 22.4-r1-s2version 22.4-r2version 22.4-r2-s1version 22.4-r2-s2version 22.4-r3version 22.4-r3-s1version 22.4-r3-s2version 22.4-r3-s3version 22.4-r3-s4version 22.4-r3-s5version 22.4-r3-s6version 22.4-r3-s7version 22.4-r3-s9version 23.1version 23.1-r1version 23.1-r2version 23.1-r3version 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-s3version 23.2-r2-s4version 23.2-r2-s5version 23.2-r2-s6version 23.4version 23.4-r1version 23.4-r1-s1version 23.4-r1-s2version 23.4-r2version 23.4-r2-s1version 23.4-r2-s2version 23.4-r2-s3version 23.4-r2-s4version 23.4-r2-s5version 23.4-r2-s6version 23.4-r2-s7	Vulnerable	NIST National Vulnerability Database
Juniper Networks	Junos Os Evolved	≥ 23.2 and < 23.2R2-S7-EVO≥ 23.4 and < 23.4R2-S8-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

Local

Attack complexity

Low

Privileges required

High

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
6.7	CVSS 4.0	Medium	—	—	sirt@juniper.net via NIST National Vulnerability Database
6.7	CVSS 4.0	Medium	—	—	juniper via CVE Program (cve.org) e CISA ADP
4.4	CVSS 3.1	Medium	0.8	3.6	sirt@juniper.net via NIST National Vulnerability Database
4.4	CVSS 3.1	Medium	—	—	juniper via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:L/AC:L/PR:H/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-476 · NULL Pointer Dereference

Other CVEs with this weakness →

Detection

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

Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.

endpoint 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 15, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 15, 2026
Fix documented
Oct 15, 2026 · NIST National Vulnerability Database
CVSS changed · 4.4
Oct 15, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 15, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 15, 2026 · NIST National Vulnerability Database
CVE published
Jul 9, 2026 · juniper

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

2 on the record

supportportal.juniper.net/JSA110072
Vendor Advisory, vendor-advisory, NIST National Vulnerability Database
github.com/orangecertcc/security-research/security/advisories/GHSA-g4f7-w2rc-hpj
Mitigation, Exploit, Third Party Advisory, third-party-advisory, NIST National Vulnerability Database

Elsewhere on this site

Juniper Networks
every CVE for this vendor

Memory corruption
same class

CWE-476
other pages naming this weakness

Related CVEs (same products)

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 1d
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 1d
Critical CVE-2026-101983 Junos OS and Junos OS Evolved: An attacker causes remote code execution when J-Web virtual-domain is configured 1d
Medium CVE-2026-101964 Junos OS and Junos OS Evolved: An attacker can cause an rpd crash via a crafted LDP message 1d
Medium CVE-2026-101975 Junos OS and Junos OS Evolved: Improper OSPF LSA validation causes an rpd crash when prefix-SID best-route installation is used 1d
Medium CVE-2026-101972 Junos OS and Junos OS Evolved: Malformed OSPF packets causes routing disruption when OSPF is enabled 1d

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 FIRST EPSS score.
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-2026-21901 is "Junos OS and Junos OS Evolved: Configuration of a specific SSH option results in mgd 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 4.4 describes technical severity. 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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