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(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.

Published: 2026-01-15 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-21911 is rated Low Risk (33.2/100): CVSS High severity, with low exploitation likelihood (EPSS 0.22%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-21911

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.02% 0.22% +0.21%
2 2026-01-16 — 0.02% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-21911

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.1 4.0 HIGH
CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/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:A/V:C/RE:M/U:Amber Click to expand
Attack vector (AV:A)
Attacker has to be on an adjacent/local network segment.
Attack complexity (AC:L)
Exploitation conditions are straightforward and stable.
Attack requirements (AT:N)
No additional preconditions are required beyond normal reachability.
Privileges required (PR:N)
No privileges are required.
User interaction (UI:N)
No user interaction is required.
Vulnerable system confidentiality impact (VC:N)
No confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:N)
No integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:H)
High availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:N)
No confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:N)
No integrity impact on subsequent systems.
Subsequent system availability impact (SA:L)
Limited availability impact on subsequent systems.
Exploit maturity (threat) (E:X)
Not defined: no reliable threat intelligence; scoring assumes the worst case (equivalent to Attacked).
Confidentiality requirement (CR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Integrity requirement (IR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Availability requirement (AR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Modified attack vector (MAV:X)
Not defined: scoring uses the Base Attack Vector (AV).
Modified attack complexity (MAC:X)
Not defined: scoring uses the Base Attack Complexity (AC).
Modified attack requirements (MAT:X)
Not defined: scoring uses the Base Attack Requirements (AT).
Modified privileges required (MPR:X)
Not defined: scoring uses the Base Privileges Required (PR).
Modified user interaction (MUI:X)
Not defined: scoring uses the Base User Interaction (UI).
Modified vulnerable system confidentiality impact (MVC:X)
Not defined: scoring uses the Base VC metric.
Modified vulnerable system integrity impact (MVI:X)
Not defined: scoring uses the Base VI metric.
Modified vulnerable system availability impact (MVA:X)
Not defined: scoring uses the Base VA metric.
Modified subsequent system confidentiality impact (MSC:X)
Not defined: scoring uses the Base SC metric.
Modified subsequent system integrity impact (MSI:X)
Not defined: scoring uses the Base SI metric.
Modified subsequent system availability impact (MSA:X)
Not defined: scoring uses the Base SA metric.
Safety (supplemental) (S:X)
Not evaluated.
Automatable (supplemental) (AU:Y)
Yes: all four kill-chain steps (reconnaissance, weaponization, delivery, exploitation) can be automated.
Recovery (supplemental) (R:A)
Automatic: services recover on their own after an attack.
Value density (supplemental) (V:C)
Concentrated: a single exploit event controls rich resources (e.g., a central server).
Vulnerability response effort (supplemental) (RE:M)
Moderate effort (remote update, disable subsystem, simple upgrade with minor service impact).
Provider urgency (supplemental) (U:AMBER)
Amber: provider rates moderate urgency.
 — — [email protected]
6.5 3.1 MEDIUM
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:A)
Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 3.6 [email protected]

Weakness enumeration for CVE-2026-21911

Affected software / configurations for CVE-2026-21911

Vendor Product Version Raw CPE
juniper junos_os_evolved < 21.4 cpe:2.3:o:juniper:junos_os_evolved:*:*:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:-:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r1:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r1-s1:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r1-s2:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r2:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r2-s1:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r2-s2:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r3:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r3-s1:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r3-s2:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r3-s3:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r3-s4:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r3-s5:*:*:*:*:*:*
juniper junos_os_evolved 21.4 cpe:2.3:o:juniper:junos_os_evolved:21.4:r3-s6:*:*:*:*:*:*
juniper junos_os_evolved 22.2 cpe:2.3:o:juniper:junos_os_evolved:22.2:-:*:*:*:*:*:*
juniper junos_os_evolved 22.2 cpe:2.3:o:juniper:junos_os_evolved:22.2:r1:*:*:*:*:*:*
juniper junos_os_evolved 22.2 cpe:2.3:o:juniper:junos_os_evolved:22.2:r1-s1:*:*:*:*:*:*
juniper junos_os_evolved 22.2 cpe:2.3:o:juniper:junos_os_evolved:22.2:r1-s2:*:*:*:*:*:*
juniper junos_os_evolved 22.2 cpe:2.3:o:juniper:junos_os_evolved:22.2:r2:*:*:*:*:*:*
juniper junos_os_evolved 22.2 cpe:2.3:o:juniper:junos_os_evolved:22.2:r2-s1:*:*:*:*:*:*
juniper junos_os_evolved 22.2 cpe:2.3:o:juniper:junos_os_evolved:22.2:r2-s2:*:*:*:*:*:*
juniper junos_os_evolved 22.2 cpe:2.3:o:juniper:junos_os_evolved:22.2:r3:*:*:*:*:*:*
juniper junos_os_evolved 22.2 cpe:2.3:o:juniper:junos_os_evolved:22.2:r3-s1:*:*:*:*:*:*
juniper junos_os_evolved 22.2 cpe:2.3:o:juniper:junos_os_evolved:22.2:r3-s2:*:*:*:*:*:*
juniper junos_os_evolved 22.2 cpe:2.3:o:juniper:junos_os_evolved:22.2:r3-s3:*:*:*:*:*:*
juniper junos_os_evolved 22.3 cpe:2.3:o:juniper:junos_os_evolved:22.3:-:*:*:*:*:*:*
juniper junos_os_evolved 22.3 cpe:2.3:o:juniper:junos_os_evolved:22.3:r1:*:*:*:*:*:*
juniper junos_os_evolved 22.3 cpe:2.3:o:juniper:junos_os_evolved:22.3:r1-s1:*:*:*:*:*:*
juniper junos_os_evolved 22.3 cpe:2.3:o:juniper:junos_os_evolved:22.3:r1-s2:*:*:*:*:*:*
juniper junos_os_evolved 22.3 cpe:2.3:o:juniper:junos_os_evolved:22.3:r2:*:*:*:*:*:*
juniper junos_os_evolved 22.3 cpe:2.3:o:juniper:junos_os_evolved:22.3:r2-s1:*:*:*:*:*:*
juniper junos_os_evolved 22.3 cpe:2.3:o:juniper:junos_os_evolved:22.3:r2-s2:*:*:*:*:*:*
juniper junos_os_evolved 22.3 cpe:2.3:o:juniper:junos_os_evolved:22.3:r3:*:*:*:*:*:*
juniper junos_os_evolved 22.3 cpe:2.3:o:juniper:junos_os_evolved:22.3:r3-s1:*:*:*:*:*:*
juniper junos_os_evolved 22.3 cpe:2.3:o:juniper:junos_os_evolved:22.3:r3-s2:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:-:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r1:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r1-s1:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r1-s2:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r2:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r2-s1:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r2-s2:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r3:*:*:*:*:*:*
juniper junos_os_evolved 22.4 cpe:2.3:o:juniper:junos_os_evolved:22.4:r3-s1:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:-:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r1:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r1-s1:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r1-s2:*:*:*:*:*:*
juniper junos_os_evolved 23.2 cpe:2.3:o:juniper:junos_os_evolved:23.2:r2:*:*:*:*:*:*
juniper junos_os_evolved 23.4 cpe:2.3:o:juniper:junos_os_evolved:23.4:-:*:*:*:*:*:*
juniper junos_os_evolved 23.4 cpe:2.3:o:juniper:junos_os_evolved:23.4:r1:*:*:*:*:*:*
juniper junos_os_evolved 23.4 cpe:2.3:o:juniper:junos_os_evolved:23.4:r1-s1:*:*:*:*:*:*
juniper junos_os_evolved 23.4 cpe:2.3:o:juniper:junos_os_evolved:23.4:r2:*:*:*:*:*:*

References for CVE-2026-21911

cvelogic Threat Intelligence