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NVD / CVE Program· CNA juniper

CVE-2026-21910: Junos OS: EX4k Series, QFX5k Series: In an EVPN-VXLAN configuration link flaps cause Inter-VNI traffic drop

Noroxi assessment

Priority: Monitor (action score 28/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.26% (FIRST EPSS).
  • Someone on the same network segment can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Juniper Networks Junos OS 21.4R3-S12, 22.2*, 22.4R3-S8.

Low priority for now. Upgrade to Juniper Networks Junos OS 21.4R3-S12, 22.2*, 22.4R3-S8 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (PFE) of Juniper Networks Junos OS on EX4k Series and QFX5k Series platforms allows an unauthenticated network-adjacent attacker flapping an interface to cause traffic between VXLAN Network Identifiers (VNIs) to drop, leading to a Denial of Service (DoS). On all EX4k and QFX5k platforms, a link flap in an EVPN-VXLAN configuration Link Aggregation Group (LAG) results in Inter-VNI traffic dropping when there are multiple load-balanced next-hop routes for the same destination. This issue is only applicable to systems that support EVPN-VXLAN Virtual Port-Link Aggregation Groups (VPLAG), such as the QFX5110, QFX5120, QFX5200, EX4100, EX4300, EX4400, and EX4650. Service can only be restored by restarting the affected FPC via the 'request chassis fpc restart slot <slot-number>' command. This issue affects Junos OS on EX4k and QFX5k Series:  * all versions before 21.4R3-S12,  * all versions of 22.2 * from 22.4 before 22.4R3-S8,  * from 23.2 before 23.2R2-S5,  * from 23.4 before 23.4R2-S5,  * from 24.2 before 24.2R2-S3, * from 24.4 before 24.4R2.

HighCVSS 7.1 · v4.0—No exploit Fix available
Published
Jan 15, 2026
Updated
Jun 17, 2026
EPSS
0.2% · 18th percentile

Report tools

JSON

Action score

28

Monitor

Low priority for now.

CVSS
28 / 40 · 7.1 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · juniper
6.5
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-21910

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
juniperjunos
juniperex4000
juniperex4100
juniperex4100-f
juniperex4100-h
juniperex4300
juniperex4400
juniperex4600
juniperex4650
juniperqfx5110
juniperqfx5120
juniperqfx5130

and 7 more

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • juniper junosbefore 21.4
  • juniper junos21.4
  • juniper junos22.2
  • juniper junos22.4
  • juniper junos23.2
  • juniper junos23.4
  • juniper junos24.2
  • juniper junos24.4

Versions reported by the vendor

Affected version ranges reported by the assigning authority (juniper). Independent of NVD's CPE analysis and usually ahead of it.

  • Juniper Networks Junos OS

    • before 21.4R3-S12affected · semver
    • 22.2 and later · before 22.2*affected · semver
    • 22.4 and later · before 22.4R3-S8affected · semver
    • 23.2 and later · before 23.2R2-S5affected · semver
    • 23.4 and later · before 23.4R2-S5affected · semver
    • 24.2 and later · before 24.2R2-S3affected · semver
    • 24.4 and later · before 24.4R2affected · semver

Same product

juniper: all records

Other highest-scoring records for the same primary product.

  • CVE-2023-36845Junos OS: EX and SRX Series: A PHP vulnerability in J-Web allows an unauthenticated to control an important environment variableKEV
    98Now
  • CVE-2023-36846Junos OS: SRX Series: A vulnerability in J-Web allows an unauthenticated attacker to upload arbitrary filesKEV
    79This week
  • CVE-2023-36844Junos OS: EX Series: A PHP vulnerability in J-Web allows an unauthenticated attacker to control important environment variablesKEV
    78This week

Published before and after this one in the same product

  • ← EarlierCVE-2026-21908Jan 15, 2026 · Junos OS and Junos OS Evolved: Use after free vulnerability In 802.1X authentication daemon can cause crash of the dot1xd process
    30Monitor
  • ← EarlierCVE-2026-21909Jan 15, 2026 · Junos OS and Junos OS Evolved: Receipt of specific IS-IS update packet causes memory leak leading to RPD crash
    28Monitor
  • Later →CVE-2026-21912Jan 15, 2026 · Junos OS: MX10k Series: 'show system firmware' CLI command may lead to LC480 or LC2101 line card reset
    27Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Juniper Networks Junos OS21.4R3-S12Vendor (CNA)
Juniper Networks Junos OS22.2*Vendor (CNA)
Juniper Networks Junos OS22.4R3-S8Vendor (CNA)
Juniper Networks Junos OS23.2R2-S5Vendor (CNA)
Juniper Networks Junos OS23.4R2-S5Vendor (CNA)
Juniper Networks Junos OS24.2R2-S3Vendor (CNA)
Juniper Networks Junos OS24.4R2Vendor (CNA)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-3379084 days apartJunos OS: SRX Series: In a NAT64 configuration, receipt of a specific, malformed ICMPv6 packet will cause the srxpfe process to crash and restart.
    34Monitor
  • CVE-2025-6000498 days apartJunos OS and Junos OS Evolved: Specific BGP EVPN update message causes rpd crash
    34Monitor
  • CVE-2025-52981188 days apartJunos OS: SRX Series: Sequence of specific PIM packets causes a flowd crash
    34Monitor
  • CVE-2025-21594281 days apartJunos OS: MX Series: In DS-lite and NAT scenario receipt of crafted IPv6 traffic causes port block
    34Monitor
  • CVE-2025-30660281 days apartJunos OS: MX Series: Decapsulation of specific GRE packets leads to PFE reset
    34Monitor
  • CVE-2024-47499461 days apartJunos OS and Junos OS Evolved: In a BMP scenario receipt of a malformed AS PATH attribute can cause an RPD crash
    34Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone on the same network segment can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Adjacent
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-754 · Improper Check for Unusual or Exceptional Conditions

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:U/V:X/RE:M/U:Green

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

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References

Show all references (1 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records