CVE-2026-21911: Junos OS Evolved: Flapping management interface causes MAC learning on label-switched interfaces to stop
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(REASONNONE) i-op:6(INTRNLOPHWFORCEDELETE) status:10 lstatus:10 err:26(GETIFBDVALIDATEFAILED) err-reason 4(IFBDVALIDATEFAILEPOCHMISMATCH) hwwr:0x4 ctxsync:0 fwdsync:0 rtt-id:51 pifl:0 fwdnh: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:GETMAC, ALLOCATEMAC, GETIFL, GETIFF, GETIFBD, 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.
Affected Software
Remediation
Information
Event History
Frequently Asked Questions
What is the severity of CVE-2026-21911?
CVE-2026-21911 has been assigned a severity rating that indicates a significant impact on network operations due to incorrect MAC learning mechanisms.
How do I fix CVE-2026-21911?
To fix CVE-2026-21911, update Junos OS Evolved to a version that addresses this vulnerability.
Who is affected by CVE-2026-21911?
CVE-2026-21911 affects users of Juniper Networks Junos OS Evolved from version 21.4R3-S7-EVO and specific versions up to 23.4R1-S2-EVO.
What are the implications of CVE-2026-21911?
The implications of CVE-2026-21911 include the risk of disrupted network connectivity due to failures in MAC learning on label-switched interfaces.
Is there a workaround for CVE-2026-21911?
Currently, no specific workarounds are documented for CVE-2026-21911 beyond upgrading to a patched version.