CVE-2026-21919 — Junos OS and Junos OS Evolved: A high frequency of connecting and disconnecting NETCONF sessions causes management unavailability
An Incorrect Synchronization vulnerability in the management daemon (mgd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker with low privileges to cause a complete Denial-of-Service (DoS) of the management plane. When NETCONF sessions are quickly established and disconnected, a locking issue causes mgd processes to hang in an unusable state. When the maximum number of mgd processes has been reached, no new logins are possible. This leads to the inability to manage the device and requires a power-cycle to recover. This issue can be monitored by checking for mgd processes in lockf state in the output of 'show system processes extensive': user@host> show system processes extensive | match mgd <pid> root 20 0 501M 4640K lockf 1 0:01 0.00% mgd If the system still can be accessed (either via the CLI or as root, which might still be possible as last resort as this won't invoke mgd), mgd processes in this state can be killed with 'request system process terminate <PID>' from the CLI or with 'kill -9 <PID>' from the shell. This issue affects: Junos OS: * 23.4 versions before 23.4R2-S4, * 24.2 versions before 24.2R2-S1, * 24.4 versions before 24.4R1-S3, 24.4R2; This issue does not affect Junos OS versions before 23.4R1; Junos OS Evolved: * 23.4 versions before 23.4R2-S5-EVO, * 24.2 versions before 24.2R2-S1-EVO, * 24.4 versions before 24.4R1-S3-EVO, 24.4R2-EVO. This issue does not affect Junos OS Evolved versions before 23.4R1-EVO;
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.2% (30-day exploitation probability)+2
- 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.
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.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Documented mitigation — kb.juniper.net (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, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Juniper Networks | Junos |
version 23.4-r1version 23.4version 24.4-r2version 24.4-r1-s2version 24.4-r1version 24.4version 24.2-r2version 24.2-r1-s2 and 9 moreversion 24.2-r1-s1version 24.2version 23.4-r2-s3version 23.4-r2-s2version 23.4-r2-s1version 23.4-r2version 23.4-r1-s2version 23.4-r1-s1version 24.2-r1 |
Vulnerable | NIST National Vulnerability Database |
| Juniper Networks | Junos OS | ≥ 24.4 and < 24.4R1-S3, 24.4R2≥ 24.2 and < 24.2R2-S1≥ 23.4 and < 23.4R2-S4 | Vulnerable | CVE Program (cve.org) e CISA ADP |
| Juniper Networks | Junos Os Evolved | ≥ 24.4 and < 24.4R1-S3-EVO, 24.4R2-EVO≥ 24.2 and < 24.2R2-S1-EVO≥ 23.4 and < 23.4R2-S5-EVO | Vulnerable | CVE Program (cve.org) e CISA ADP |
| Juniper Networks | Junos Os Evolved |
version 24.4-r2version 24.4-r1-s2version 24.4-r1version 24.4version 24.2-r2version 24.2-r1-s2version 24.2-r1version 24.2 and 9 moreversion 23.4-r2-s4version 23.4-r2-s3version 23.4-r2-s2version 23.4-r2-s1version 23.4-r2version 23.4-r1-s2version 23.4-r1-s1version 23.4-r1version 23.4 |
Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
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.
EPSS over time FIRST
Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 0.23%
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).
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · juniper networks/junos os, juniper networks/junos os evolved
- SSVC assessment updated
- Record published
- Fix documented
- CVSS changed · 6.5
- Source status changed · → Analyzed
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
1 on the record
Elsewhere on this site
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 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
- 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
- Medium CVE-2026-101964 Junos OS and Junos OS Evolved: An attacker can cause an rpd crash via a crafted LDP message 1d
- High CVE-2026-101981 Junos OS and Junos OS Evolved: An adjacent LDP peer causes routing-engine compromise when LDP is enabled 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 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-2026-21919 is "Junos OS and Junos OS Evolved: A high frequency of connecting and disconnecting NETCONF sessions causes management unavailability", 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 0.23% 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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