Junos OS and Junos OS Evolved: A high frequency of connecting and disconnecting NETCONF sessions causes management unavailability
Summary
| CVE | CVE-2026-21919 |
|---|---|
| State | PUBLISHED |
| Assigner | juniper |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-04-09 22:16:25 UTC |
| Updated | 2026-04-17 18:04:47 UTC |
| Description | 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; |
Risk And Classification
Primary CVSS: v4.0 7.1 HIGH from [email protected]
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/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:U/V:X/RE:M/U:X
EPSS: 0.000450000 probability, percentile 0.136250000 (date 2026-04-21)
Problem Types: CWE-821 | CWE-821 CWE-821 Incorrect Synchronization
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | [email protected] | Secondary | 7.1 | 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:N/E:X/C... |
| 4.0 | CNA | CVSS | 7.1 | 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:N/AU:Y/... |
| 3.1 | [email protected] | Primary | 6.5 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
| 3.1 | CNA | CVSS | 6.5 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
CVSS v4.0 Breakdown
Attack Vector
NetworkAttack Complexity
LowAttack Requirements
NonePrivileges Required
LowUser Interaction
NoneConfidentiality
NoneIntegrity
NoneAvailability
HighSub Conf.
NoneSub Integrity
NoneSub Availability
NoneCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/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:U/V:X/RE:M/U:X
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
LowUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
NoneAvailability
HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD Known Affected Configurations (CPE 2.3)
| Type | Vendor | Product | Version | Update | Edition | Language |
|---|---|---|---|---|---|---|
| Operating System | Juniper | Junos | 23.4 | - | All | All |
| Operating System | Juniper | Junos | 23.4 | r1 | All | All |
| Operating System | Juniper | Junos | 23.4 | r1-s1 | All | All |
| Operating System | Juniper | Junos | 23.4 | r1-s2 | All | All |
| Operating System | Juniper | Junos | 23.4 | r2 | All | All |
| Operating System | Juniper | Junos | 23.4 | r2-s1 | All | All |
| Operating System | Juniper | Junos | 23.4 | r2-s2 | All | All |
| Operating System | Juniper | Junos | 23.4 | r2-s3 | All | All |
| Operating System | Juniper | Junos | 24.2 | - | All | All |
| Operating System | Juniper | Junos | 24.2 | r1 | All | All |
| Operating System | Juniper | Junos | 24.2 | r1-s1 | All | All |
| Operating System | Juniper | Junos | 24.2 | r1-s2 | All | All |
| Operating System | Juniper | Junos | 24.2 | r2 | All | All |
| Operating System | Juniper | Junos | 24.4 | - | All | All |
| Operating System | Juniper | Junos | 24.4 | r1 | All | All |
| Operating System | Juniper | Junos | 24.4 | r1-s2 | All | All |
| Operating System | Juniper | Junos | 24.4 | r2 | All | All |
| Operating System | Juniper | Junos Os Evolved | 23.4 | - | All | All |
| Operating System | Juniper | Junos Os Evolved | 23.4 | r1 | All | All |
| Operating System | Juniper | Junos Os Evolved | 23.4 | r1-s1 | All | All |
| Operating System | Juniper | Junos Os Evolved | 23.4 | r1-s2 | All | All |
| Operating System | Juniper | Junos Os Evolved | 23.4 | r2 | All | All |
| Operating System | Juniper | Junos Os Evolved | 23.4 | r2-s1 | All | All |
| Operating System | Juniper | Junos Os Evolved | 23.4 | r2-s2 | All | All |
| Operating System | Juniper | Junos Os Evolved | 23.4 | r2-s3 | All | All |
| Operating System | Juniper | Junos Os Evolved | 23.4 | r2-s4 | All | All |
| Operating System | Juniper | Junos Os Evolved | 24.2 | - | All | All |
| Operating System | Juniper | Junos Os Evolved | 24.2 | r1 | All | All |
| Operating System | Juniper | Junos Os Evolved | 24.2 | r1-s2 | All | All |
| Operating System | Juniper | Junos Os Evolved | 24.2 | r2 | All | All |
| Operating System | Juniper | Junos Os Evolved | 24.4 | - | All | All |
| Operating System | Juniper | Junos Os Evolved | 24.4 | r1 | All | All |
| Operating System | Juniper | Junos Os Evolved | 24.4 | r1-s2 | All | All |
| Operating System | Juniper | Junos Os Evolved | 24.4 | r2 | All | All |
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Juniper Networks | Junos OS | affected 23.4 23.4R2-S4 semver | Not specified |
| CNA | Juniper Networks | Junos OS | affected 24.2 24.2R2-S1 semver | Not specified |
| CNA | Juniper Networks | Junos OS | affected 24.4 24.4R1-S3, 24.4R2 semver | Not specified |
| CNA | Juniper Networks | Junos OS | unaffected all version prior to 23.4R1 semver | Not specified |
| CNA | Juniper Networks | Junos OS Evolved | affected 23.4 23.4R2-S5-EVO semver | Not specified |
| CNA | Juniper Networks | Junos OS Evolved | affected 24.2 24.2R2-S1-EVO semver | Not specified |
| CNA | Juniper Networks | Junos OS Evolved | affected 24.4 24.4R1-S3-EVO, 24.4R2-EVO semver | Not specified |
| CNA | Juniper Networks | Junos OS Evolved | unaffected all version prior to 23.4R1-EVO semver | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| kb.juniper.net/JSA106019 | [email protected] | kb.juniper.net | Mitigation, Vendor Advisory |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
Additional Advisory Data
Solutions
CNA: The following software releases have been updated to resolve this specific issue: Junos OS Evolved: 23.4R2-S5-EVO, 24.2R2-S1-EVO, 24.4R1-S3-EVO, 24.4R2-EVO, 25.2R1-EVO, and all subsequent releases; Junos OS: 23.4R2-S4, 24.2R2-S1, 24.4R1-S3, 24.4R2, 25.2R1, and all subsequent releases.
Workarounds
CNA: Use access lists or firewall filters to limit access to the device only from trusted hosts and administrators. To further reduce the risk of exploitation you can set values as low as needed for your normal operations for: [ system services netconf ssh connection-limit <max_connections> ] [ system services netconf ssh rate-limit <connections_per_minute> ]
Exploits
CNA: Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
There are currently no legacy QID mappings associated with this CVE.