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JunosOperating system · Juniper

CVE-2026-57027

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
A Missing Release of Memory after Effective Lifetime vulnerability in the packet forwarding engine (pfe) of Juniper Networks Junos OS on specific EX Series devices allows an unauthenticated adjacent attacker to cause a Denial-of-Service (DoS).When sFlow is configured in a Virtual Chassis (VC) scenario with EX4100 Series or EX4400 Series devices, multicast traffic which is received on one VC member and sent out on another member leads to a memory leak and ultimately an FPC crash and restart. The leak can be monitored by watching the continuous increase of the buffer values in the output of: user@host> show chassis fpc This issue affects Junos OS on EX4100 Series and EX4400: * all versions before 23.2R2-S7, * 23.4 versions before 23.4R2-S7, * 24.2 versions before 24.2R2-S4, * 24.4 versions before 24.4R2.

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 memory leak vulnerability exists in the packet forwarding engine (pfe) of Juniper EX4100 and EX4400 Series switches when sFlow is configured in a Virtual Chassis scenario. Multicast traffic received on one VC member and sent to another member causes memory that is not properly released, leading to buffer exhaustion and eventual FPC crash and restart.

MitigationUpgrade Junos OS on affected EX4100/EX4400 devices to the fixed versions (23.2R2-S7, 23.4R2-S7, 24.2R2-S4, or 24.4R2). Until upgraded, monitor FPC buffer values using 'show chassis fpc' and consider disabling sFlow in VC if feasible.

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. Confirm device model is EX4100 or EX4400
    Run 'show chassis hardware' or 'show version' to identify the device model
    Affected if Device is not an EX4100 or EX4400 series switch - this CVE only affects those specific models
  2. Verify Junos version is in affected range
    Run 'show version' and check the Junos OS version against: < 23.2, = 23.2, = 23.4, = 24.2, = 24.4
    Affected if Junos version matches any of the listed vulnerable versions (< 23.2, 23.2, 23.4, 24.2, or 24.4)
  3. Confirm Virtual Chassis is configured
    Run 'show virtual-chassis' to check if the switch is part of a Virtual Chassis configuration
    Affected if Virtual Chassis is not configured - the vulnerability only triggers in VC scenarios with multicast traffic between members
  4. Verify sFlow is enabled
    Run 'show sflow' or check configuration with 'show configuration protocols sflow'
    Affected if sFlow is not enabled - the memory leak only occurs when sFlow is configured in the VC scenario
  5. Check FPC buffer health for signs of exhaustion
    Run 'show chassis fpc' and look for high buffer utilization or FPC restart indicators
    Affected if FPC shows abnormal buffer usage, frequent restarts, or crash history consistent with memory exhaustion

A user is affected if they have an EX4100 or EX4400 switch running a vulnerable Junos version (23.2, 23.4, 24.2, or 24.4) with both Virtual Chassis and sFlow configured, and they are seeing FPC buffer issues or crashes.

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 affected EX4100/EX4400 devices to the fixed versions (23.2R2-S7, 23.4R2-S7, 24.2R2-S4, or 24.4R2). Until upgraded, monitor FPC buffer values using 'show chassis fpc' and consider disabling sFlow in VC if feasible.

Recommended fix High confidence

23.2R2-S7, 23.4R2-S7, 24.2R2-S4, or 24.4R2 (or later versions in those branches)

  1. 1. Identify the current Junos OS version on the EX4100 or EX4400 device using 'show version'
  2. 2. Verify sFlow is configured in a Virtual Chassis scenario using 'show configuration | display set | match sflow'
  3. 3. If running an affected version (< 23.2R2-S7, < 23.4R2-S7, < 24.2R2-S4, or < 24.4R2), plan for upgrade to a fixed version
  4. 4. Download the appropriate fixed Junos OS release (23.2R2-S7 or later, 23.4R2-S7 or later, 24.2R2-S4 or later, or 24.4R2 or later) from the Juniper support portal
  5. 5. Back up the current device configuration using 'request system configuration rescue save'
  6. 6. Upgrade the device using 'request system software add <package-name>' or follow standard Junos upgrade procedures
  7. 7. After upgrade, verify the new version is installed using 'show version'
  8. 8. Monitor for memory leak by checking 'show chassis fpc' output to confirm buffer values stabilize
Caveat Standard Junos upgrade precautions apply - review release notes for any known issues and ensure compatibility with existing network configuration

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

Fix this in Junos Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,980
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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-2026-57027 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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