CVE-2026-21911 - Junos OS Evolved Plugin
CVE-2026-21911
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.
CVE-2026-21911
HIGH
CVSS 7.1
Published 2026-01-15
Updated 2026-01-23
AI Risk High (84/100)
Active Exploit: No strong signal
Published Exploit: Possible PoC indicators
Priority: P2 Urgent
Severity Band
HIGH
CVSS Vector
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
Affected Components
1
Reference Links
2
AI Risk Engine
High (84/100)
Exploitability
High
Active Exploitation
No strong signal
Published Exploit Status
Possible PoC indicators
AI Context
Machine-generated threat intelligence
AI
Updated 12 days ago
AI enriched 12 days ago (2026-04-09 08:01 UTC)
Technical Summary
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…
Potential Impact
Severity is HIGH (CVSS 7.1). Depending on deployment context, affected components may be exposed to unauthorized actions or data integrity risk.
Exploitability Assessment
Exploitability is assessed as High based on remote code execution potential, low-bar exploit prerequisites.
Primary risk drivers: remote code execution potential, low-bar exploit prerequisites
Mitigation Recommendations
Validate affected product versions, prioritize patching, and monitor references for vendor remediation guidance. If immediate patching is not possible, apply compensating controls and limit exposure of vulnerable surfaces.
Detection & Monitoring
Track authentication anomalies, unexpected file writes, and suspicious plugin API activity around affected components.
Business Impact Lens
Prioritize remediation where affected components process customer data, admin sessions, or Internet-exposed workflows.
