CVE-2026-21911

Junos OS Evolved: Flapping management interface causes MAC learning on label-switched interfaces to stop

MEDIUM

6.5

CVSS Score

Published: January 15, 2026 at 08:23 PM UTC

Updated: June 17, 2026 at 10:19 AM UTC

2 products affected across 2 vendorsJunos OS EvolvedJunos OS Evolved

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Severity

MEDIUM6.5

Exploit prediction

EPSS 0.2%

SSVC

No known exploit

Description

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Junos OS Evolved · Juniper Networks

60%

v < 21.4R3-S7-EVO22.2 ≤ v < 22.2R3-S4-EVO22.3 ≤ v < 22.3R3-S3-EVO22.4 ≤ v < 22.4R3-S2-EVO23.2 ≤ v < 23.2R2-S1-EVO23.4 ≤ v < 23.4R1-S2-EVO, 23.4R2-EVO22.2 22.3 22.4 23.2 23.4

Affected range stops below 21.4R3-S7-EVO, so it looks safe — our inference, not a vendor statement

Affected range stops below 22.2R3-S4-EVO, so it looks safe — our inference, not a vendor statement

Affected range stops below 22.3R3-S3-EVO, so it looks safe — our inference, not a vendor statement

Affected range stops below 22.4R3-S2-EVO, so it looks safe — our inference, not a vendor statement

Affected range stops below 23.2R2-S1-EVO, so it looks safe — our inference, not a vendor statement

Affected range stops below 23.4R1-S2-EVO, 23.4R2-EVO, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (2)

Vendor Advisory

Source: cverecord

https://supportportal.juniper.net/JSA106010

Vendor Advisory

Source: cverecord

https://kb.juniper.net/JSA106010

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.5MEDIUMjuniper

Attack Vector: ADJACENT_NETWORK
Complexity: LOW
Privileges: NONE
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: NONE
Integrity: NONE
Availability: HIGH

Vector?

Quick Info

StatusANALYZED

CWE

CWE-682

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