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JunosOperating system · Juniper

CVE-2026-57020

MEDIUM · 6.5 CVSS v3.1 Published 2026-07-09
Fix available
A fix is available. Upgrade to 23.2 or later.
See remediation →
70/100
Remediation priority · Elevated
No privileges Zero-click 6 weeks old

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 QFX10000 Series allows an unauthenticated, adjacent attacker to cause a Denial-of-Service (DoS). On all QFX10000 platforms in an EVPN-VxLAN scenario, if an attacker sends IPv6 multicast traffic and these packets reach the non-IRB interface of a spine switch it floods the packet to other spines and all Ethernet Segment Identifier (ESI) leaf switches. This flooding causes the packet to be forwarded in a endless loop, which can lead to saturation of the involved links and in turn impact to legitimate traffic. This issue affects Junos OS on QFX10000 Series: * all versions before 23.2R2-S7, * 23.4 versions before 23.4R2-S8, * 24.2 versions before 24.2R2-S4, * 24.4 versions before 24.4R2-S4. This issue does not affect Junos version after 24.4 as the QFX10000 Series devices are not supported on newer versions anymore.

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 the packet forwarding engine of Juniper Junos OS on QFX10000 switches allows IPv6 multicast traffic in EVPN-VxLAN scenarios to flood uncontrollably when reaching a spine switch's non-IRB interface. This causes packets to loop endlessly between spines and ESI leaf switches, saturating links and causing denial of service to legitimate traffic.

MitigationUpgrade Junos OS on QFX10000 devices to the fixed versions (23.2R2-S7, 23.4R2-S8, 24.2R2-S4, or 24.4R2-S4) to address the improper condition handling in the PFE.

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:< 23.2= 23.2= 23.4= 24.2= 24.4

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. Identify the device model
    Run 'show chassis hardware' or 'show version' to confirm the device is a QFX10000 series switch
    Affected if Device is NOT a QFX10000 switch - this vulnerability only affects QFX10000 switches
  2. Check the Junos OS version
    Run 'show version' and compare the installed version against the affected ranges: < 23.2, 23.2, 23.4, 24.2, or 24.4
    Affected if The installed version matches any of the affected versions listed (or is earlier than 23.2)
  3. Verify EVPN-VxLAN configuration
    Run 'show configuration evpn' and 'show configuration protocols vxlan' to see if EVPN-VxLAN is configured
    Affected if EVPN-VxLAN is NOT configured - the vulnerability requires EVPN-VxLAN to be in use
  4. Confirm IPv6 multicast forwarding is active
    Run 'show multicast interfaces' or 'show pim interfaces' to check for IPv6 multicast-enabled interfaces in the EVPN-VxLAN topology
    Affected if IPv6 multicast forwarding is NOT enabled - the flaw specifically affects IPv6 multicast traffic in EVPN-VxLAN
  5. Check for non-IRB spine interfaces in EVPN topology
    Run 'show evpn instance' and 'show interface terse' to identify spine switch configurations - look for non-IRB (non-integrated routing and bridging) interfaces participating in EVPN
    Affected if Spine switches use ONLY IRB interfaces (no non-IRB interfaces) - the flaw triggers when traffic reaches a non-IRB interface on the spine

A device is affected if it is a QFX10000 switch running a vulnerable Junos version (23.2, 23.4, 24.2, 24.4, or any version earlier than 23.2), has EVPN-VxLAN configured with IPv6 multicast forwarding, and contains non-IRB interfaces on spine switches in the topology.

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
Upgrade available Upgrade to 23.2 or later
Fixed in 23.2
Interim mitigation

Upgrade Junos OS on QFX10000 devices to the fixed versions (23.2R2-S7, 23.4R2-S8, 24.2R2-S4, or 24.4R2-S4) to address the improper condition handling in the PFE.

Recommended fix High confidence

Upgrade to 23.2R2-S7 or later (23.2.x), 23.4R2-S8 or later (23.4.x), 24.2R2-S4 or later (24.2.x), or 24.4R2-S4 or later (24.4.x) depending on current version branch

  1. 1. Identify the current Junos OS version on the QFX10000 Series device using 'show version' command
  2. 2. Based on current version, determine the minimum fixed release needed: for 23.2.x upgrade to 23.2R2-S7 or later; for 23.4.x upgrade to 23.4R2-S8 or later; for 24.2.x upgrade to 24.2R2-S4 or later; for 24.4.x upgrade to 24.4R2-S4 or later
  3. 3. Download the appropriate fixed Junos OS release from the Juniper support portal
  4. 4. Upload the new Junos OS image to the device using 'request system software add' or through the firmware update process
  5. 5. Reboot the device to apply the new software version using 'request system reboot'
  6. 6. After reboot, verify the new version is running with 'show version'
  7. 7. In an EVPN-VxLAN topology, test by sending IPv6 multicast traffic to confirm the endless loop issue is resolved and traffic flows correctly
  8. 8. Monitor network links to ensure flooding loops are no longer occurring
Caveat Standard Junos upgrade risks apply - ensure compatibility with other devices in the EVPN-VxLAN topology and have a rollback plan; QFX10000 Series is not supported on versions after 24.4

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

Fix this in Junos Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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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

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Peer-ranked notes from engineers who’ve handled CVE-2026-57020 in production — separate from our analysis above.

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