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JunosOperating system · Juniper

CVE-2026-33781

MEDIUM · 6.5 CVSS v3.1 Published 2026-04-09
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
70/100
Remediation priority · Elevated
No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (pfe) of Juniper Networks Junos OS on specific EX and QFX Series devices allow an unauthenticated, adjacent attacker to cause a complete Denial of Service (DoS). On EX4k, and QFX5k platforms configured as service-provider edge devices, if L2PT is enabled on the UNI and VSTP is enabled on NNI in VXLAN scenarios, receiving VSTP BPDUs on UNI leads to packet buffer allocation failures, resulting in the device to not pass traffic anymore until it is manually recovered with a restart.This issue affects Junos OS: * 24.4 releases before 24.4R2, * 25.2 releases before 25.2R1-S1, 25.2R2. This issue does not affect Junos OS releases before 24.4R1.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A vulnerability in Juniper Networks Junos OS packet forwarding engine on EX4k and QFX5k platforms allows an adjacent attacker to cause complete DoS. When L2PT is enabled on UNI and VSTP is enabled on NNI in VXLAN scenarios, receiving VSTP BPDUs on UNI triggers packet buffer allocation failures, halting all traffic until manual device restart.

MitigationUpgrade Junos OS to 24.4R2 or later, or 25.2R1-S1/25.2R2 or later. Alternatively, disable L2PT on UNI or VSTP on NNI in affected VXLAN configurations until patching is possible.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
JunosOperating system
Affected:= 24.4= 25.2

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Verify device platform is affected
    Run 'show chassis hardware' or 'show system information' to confirm the device model is EX4k or QFX5k series
    Affected if Device is not an EX4k or QFX5k platform - not affected
  2. Check Junos OS version
    Run 'show version' to obtain the installed Junos OS version and compare to affected versions 24.4 and 25.2
    Affected if Version is not exactly 24.4 or 25.2 - not affected
  3. Verify L2PT configuration on UNI interfaces
    Run 'show protocols l2pt' and check interface configurations for L2PT enabled on User Network Interface (UNI) ports
    Affected if L2PT is not enabled on any UNI interfaces - not affected
  4. Verify VSTP configuration on NNI interfaces
    Run 'show protocols vstp' and check interface configurations for VSTP enabled on Network-to-Network Interface (NNI) ports
    Affected if VSTP is not enabled on any NNI interfaces - not affected
  5. Confirm VXLAN configuration exists
    Run 'show configuration vxlan' to verify VXLAN is configured on the device
    Affected if VXLAN is not configured - not affected

Device is affected only if it is EX4k or QFX5k running exactly Junos 24.4 or 25.2 with L2PT enabled on UNI, VSTP enabled on NNI, and VXLAN configured - all conditions must be true for the vulnerability to be exploitable.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Junos OS to 24.4R2 or later, or 25.2R1-S1/25.2R2 or later. Alternatively, disable L2PT on UNI or VSTP on NNI in affected VXLAN configurations until patching is possible.

Recommended fix High confidence

24.4R2 or later; or 25.2R1-S1/25.2R2 or later

  1. 1. Identify the current Junos OS version on affected EX4k and QFX5k devices using 'show version'
  2. 2. If running 24.4.x, upgrade to 24.4R2 or later
  3. 3. If running 25.2.x, upgrade to 25.2R1-S1, 25.2R2, or later
  4. 4. After upgrade, verify the device is passing traffic normally with 'show interfaces terse'
  5. 5. Confirm VSTP over L2PT functionality is working as expected
Caveat Standard Junos upgrade risks apply - test in lab first, ensure configuration backup, plan for potential downtime

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing10.0 h
  • Review / QA5.0 h
33.0 hours of engineering $5,760
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-33781 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data