CVE-2026-21919
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedAn 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;
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceAn incorrect synchronization vulnerability in the Junos OS/Junos OS Evolved management daemon (mgd) causes a locking issue when NETCONF sessions are rapidly established and disconnected. This leaves mgd processes stuck in a lockf state, and once the maximum process count is reached, no new management logins are possible, requiring a power-cycle to recover.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data= 23.4= 24.2= 24.4= 23.4= 24.2= 24.4CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify the installed Junos versionRun 'show version' or 'show version detail' to obtain the exact Junos version installed on the deviceAffected if The version matches 23.4, 24.2, or 24.4 (any build within these release trains)
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Determine if NETCONF is enabledRun 'show configuration system services netconf' or check the configuration for 'set system services netconf'Affected if NETCONF service is configured and enabled on the device
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Check for stuck mgd processesRun 'show system processes mgd' or 'ps aux | grep mgd' to view mgd process statesAffected if Multiple mgd processes are stuck in lockf state or have accumulated beyond normal expected count
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Verify management login accessibilityAttempt to establish a new NETCONF, SSH, or console management session to the deviceAffected if New management connections fail or time out, especially after rapid prior NETCONF session churn
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Check process limits and availabilityRun 'show system processes extensive' or check 'system processes max-number' configurationAffected if The maximum allowed mgd process count has been reached with no available slots for new sessions
You are affected if your device runs Junos 23.4, 24.2, or 24.4, has NETCONF enabled, and exhibits symptoms of stuck mgd processes preventing new management logins.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade to Junos OS 23.4R2-S4/24.2R2-S1/24.4R1-S3/24.4R2 or later, or Junos OS Evolved 23.4R2-S5-EVO/24.2R2-S1-EVO/24.4R1-S3-EVO/24.4R2-EVO or later.
Junos OS: 23.4R2-S4 / 24.2R2-S1 / 24.4R1-S3 / 24.4R2; Junos OS Evolved: 23.4R2-S5-EVO / 24.2R2-S1-EVO / 24.4R1-S3-EVO / 24.4R2-EVO
- Identify the current Junos OS or Junos OS Evolved version running on the device using 'show version'
- For Junos OS: upgrade to one of the fixed versions: 23.4R2-S4, 24.2R2-S1, 24.4R1-S3, or 24.4R2
- For Junos OS Evolved: upgrade to one of the fixed versions: 23.4R2-S5-EVO, 24.2R2-S1-EVO, 24.4R1-S3-EVO, or 24.4R2-EVO
- After upgrade, verify the fix by checking mgd process status with 'show system processes extensive | match mgd' to ensure no processes are in lockf state
- Alternatively, if immediate upgrade is not possible and the device is accessible, kill stuck mgd processes using 'request system process terminate <PID>' from CLI or 'kill -9 <PID>' from shell as a temporary mitigation
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-21919 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
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