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Junos Os EvolvedOperating system · Juniper

CVE-2026-21911

MEDIUM · 6.5 CVSS v3.1 Published 2026-01-15
Fix available
A fix is available. Upgrade to 21.4 or later.
See remediation →
70/100
Remediation priority · Elevated
No privileges Zero-click

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 · unedited
An Incorrect Calculation vulnerability in the Layer 2 Control Protocol Daemon (l2cpd) of Juniper Networks Junos OS Evolved allows an unauthenticated network-adjacent attacker flapping the management interface to cause the learning of new MACs over label-switched interfaces (LSI) to stop while generating a flood of logs, resulting in high CPU usage. When the issue is seen, the following log message will be generated: op:1 flag:0x6 mac:xx:xx:xx:xx:xx:xx bd:2 ifl:13302 reason:0(REASON_NONE) i-op:6(INTRNL_OP_HW_FORCE_DELETE) status:10 lstatus:10 err:26(GETIFBD_VALIDATE_FAILED) err-reason 4(IFBD_VALIDATE_FAIL_EPOCH_MISMATCH) hw_wr:0x4 ctxsync:0 fwdsync:0 rtt-id:51 p_ifl:0 fwd_nh:0 svlbnh:0 event:- smask:0x100000000 dmask:0x0 mplsmask 0x1 act:0x5800 extf:0x0 pfe-id 0 hw-notif-ifl 13302 programmed-ifl 4294967295 pseudo-vtep underlay-ifl-idx 0 stack:GET_MAC, ALLOCATE_MAC, GET_IFL, GET_IFF, GET_IFBD, STOP, This issue affects Junos OS Evolved:  * all versions before 21.4R3-S7-EVO,  * from 22.2 before 22.2R3-S4-EVO,  * from 22.3 before 22.3R3-S3-EVO,  * from 22.4 before 22.4R3-S2-EVO,  * from 23.2 before 23.2R2-S1-EVO,  * from 23.4 before 23.4R1-S2-EVO, 23.4R2-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 confidence

A calculation bug in the Layer 2 Control Protocol Daemon (l2cpd) causes MAC address learning over label-switched interfaces to halt when an attacker rapidly flaps the management interface. This triggers a flood of logging events with GETIFBD_VALIDATE_FAILED errors showing EPOCH_MISMATCH, consuming excessive CPU resources.

MitigationApply the Junos OS Evolved software update corresponding to the affected version branch (21.4R3-S7-EVO, 22.2R3-S4-EVO, 22.3R3-S3-EVO, 22.4R3-S2-EVO, 23.2R2-S1-EVO, 23.4R1-S2-EVO, or 23.4R2-EVO). Monitor for the specified log message to confirm the issue is resolved.

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
Junos Os EvolvedOperating system
Affected:< 21.4= 21.4= 22.2= 22.3= 22.4= 23.2= 23.4

CVSS 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
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/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 checks

Work through these to decide whether this CVE applies to you.

  1. Check Junos OS Evolved version
    Run 'show version' or 'show version detail' to obtain the installed Junos OS Evolved version
    Affected if Installed version is < 21.4, = 21.4, = 22.2, = 22.3, = 22.4, = 23.2, or = 23.4
  2. Verify l2cpd daemon is running
    Run 'show system processes | match l2cpd' or check daemon status via 'request system process restart l2cpd' (will show current state)
    Affected if The l2cpd daemon is active and processing traffic
  3. Search for GETIFBD_VALIDATE_FAILED log messages
    Run 'show log messages | match GETIFBD_VALIDATE_FAILED' or 'show log messages | match EPOCH_MISMATCH' to search for the error pattern
    Affected if Log output contains GETIFBD_VALIDATE_FAILED errors showing EPOCH_MISMATCH
  4. Check MAC address learning status on label-switched interfaces
    Run 'show ethernet-switching mac-learning' or 'show l2circuit connections' to inspect MAC address learning status, especially over label-switched interfaces
    Affected if MAC address learning is halted or stalled on label-switched interfaces while functioning elsewhere

Environment is affected if running a listed Junos OS Evolved version AND l2cpd is active AND GETIFBD_VALIDATE_FAILED with EPOCH_MISMATCH errors appear in logs with symptoms of halted MAC learning.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 21.4 or later
Fixed in 21.4
Interim mitigation

Apply the Junos OS Evolved software update corresponding to the affected version branch (21.4R3-S7-EVO, 22.2R3-S4-EVO, 22.3R3-S3-EVO, 22.4R3-S2-EVO, 23.2R2-S1-EVO, 23.4R1-S2-EVO, or 23.4R2-EVO). Monitor for the specified log message to confirm the issue is resolved.

Recommended fix High confidence

For 21.4 branch: upgrade to 21.4R3-S7-EVO or later | For 22.2 branch: upgrade to 22.2R3-S4-EVO or later | For 22.3 branch: upgrade to 22.3R3-S3-EVO or later | For 22.4 branch: upgrade to 22.4R3-S2-EVO or later | For 23.2 branch: upgrade to 23.2R2-S1-EVO or later | For 23.4 branch: upgrade to 23.4R1-

  1. 1. Identify the current Junos OS Evolved version by running 'show version invoke-on all-routing-engines'
  2. 2. Based on the current version, identify the target fixed release from the upgrade path below
  3. 3. Plan maintenance window as upgrade requires system reboot
  4. 4. Download the appropriate upgrade image from Juniper support portal (requires active support contract)
  5. 5. Backup current configuration using 'request system configuration backup'
  6. 6. Validate free disk space meets requirements for upgrade
  7. 7. Execute upgrade using 'request system software add <package> reboot'
  8. 8. After reboot, verify fixed version is running with 'show version'
Caveat Standard Junos OS Evolved upgrade considerations apply - ensure compatibility with other network devices and review release notes for any behavior changes between versions

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Os Evolved Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
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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 sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-21911 in production — separate from our analysis above.

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