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JunosOperating system · Juniper

CVE-2026-57019

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 Validation of Specified Quantity in Input vulnerability in the Packet Forwarding Engine (pfe) of Juniper Networks Junos OS on MX Series allows an unauthenticated, adjacent attacker to cause a Denial-of-Service (DoS). When a specific packet is received from device in the same broadcast domain, an affected system calculates the packet size incorrectly. This causes further packet processing to fail, which triggers an FPC major error, resulting in a FPC reset impacting traffic until the FPC has automatically recovered. Affected scenarios are: MAP-T, or non-IP traffic encapsulated in IP (e.g. MPLS over GRE). When this issue happens the following logs can be observed: fpc<#> CMError: /fpc/0/pfe/0/cm/0/MQSS(0)/0/MQSS_CMERROR_LI_INT_REG_UNROLL_TAIL_LENGTH_OVF (0x2205eb), scope: pfe, category: functional, severity: major, module: MQSS(0), type: LI: Unroll TAIL length overflow, oc_category: default fpc<#> Performing action reset-fru for error /fpc/0/pfe/0/cm/0/MQSS(0)/0/MQSS_CMERROR_LI_INT_REG_UNROLL_TAIL_LENGTH_OVF (0x2205eb) in module: MQSS(0) with scope: pfe category: functional level: major, oc_category: default This issue affects Junos OS on MX Series: * all versions before 23.2R2-S6, * 23.4 versions before 23.4R2-S7, * 24.2 versions before 24.2R2-S4, * 24.4 versions before 24.4R2-S4, * 25.2 versions before 25.2R2.

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

Improper input validation in the Packet Forwarding Engine (PFE) of Juniper MX Series routers causes incorrect packet size calculation when processing specific traffic types (MAP-T or non-IP traffic encapsulated in IP like MPLS over GRE). This triggers a tail length overflow (MQSS_CMERROR_LI_INT_REG_UNROLL_TAIL_LENGTH_OVF), causing an FPC major error that forces an FPC reset, resulting in denial of service until auto-recovery.

MitigationApply Junos OS updates: 23.2R2-S6 or later, 23.4R2-S7 or later, 24.2R2-S4 or later, 24.4R2-S4 or later, or 25.2R2 or later. As an interim measure, filter or block the affected traffic types (MAP-T, MPLS over GRE) from untrusted adjacent networks.

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= 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. Confirm device is a Juniper MX Series router
    Run 'show chassis hardware' or 'show version' to identify the router model
    Affected if The device is not an MX Series router (different platforms like EX, SRX, PTX are not affected by this specific vulnerability)
  2. Check installed Junos version
    Run 'show version' and locate the Junos OS version number (e.g., 23.2R1, 24.2R1)
    Affected if The installed version is 23.2, 23.4, 24.2, 24.4, or 25.2 (exact versions), or any version lower than 23.2 (e.g., 23.1, 22.4)
  3. Verify if MAP-T feature is configured
    Run 'show configuration | match map-t' or check the NAT configuration for MAP-T mapping entries
    Affected if MAP-T (Mapping of Address and Port with Translation) is actively configured and processing traffic on the router
  4. Verify if MPLS over GRE is configured
    Run 'show configuration | match gre' and check for MPLS encapsulation over GRE tunnels in the configuration
    Affected if MPLS over GRE tunnels are configured and carrying traffic
  5. Check for FPC error messages in system logs
    Run 'show log messages | match MQSS_CMERROR_LI_INT_REG_UNROLL_TAIL_LENGTH_OVF' or search for 'FPC.*major.*error' in system logs
    Affected if The specific tail length overflow error message appears in logs, indicating the vulnerability has been triggered

A user is affected if they are running an affected Junos version (23.2, 23.4, 24.2, 24.4, 25.2 or earlier) on an MX Series router AND have MAP-T or MPLS over GRE traffic actively flowing through the device, as evidenced by FPC error logs.

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

Apply Junos OS updates: 23.2R2-S6 or later, 23.4R2-S7 or later, 24.2R2-S4 or later, 24.4R2-S4 or later, or 25.2R2 or later. As an interim measure, filter or block the affected traffic types (MAP-T, MPLS over GRE) from untrusted adjacent networks.

Recommended fix High confidence

Minimum fixed versions: 23.2R2-S6, 23.4R2-S7, 24.2R2-S4, 24.4R2-S4, or 25.2R2 (or later in respective branches)

  1. Identify the current Junos OS version on the MX Series device using 'show version'
  2. Determine which version branch the current installation belongs to (23.2, 23.4, 24.2, 24.4, or 25.2)
  3. For devices on 23.2 branch: upgrade to 23.2R2-S6 or later (e.g., 23.2R2-S7, 23.2R3)
  4. For devices on 23.4 branch: upgrade to 23.4R2-S7 or later (e.g., 23.4R3, 23.4R3-S1)
  5. For devices on 24.2 branch: upgrade to 24.2R2-S4 or later (e.g., 24.2R3)
  6. For devices on 24.4 branch: upgrade to 24.4R2-S4 or later (e.g., 24.4R3)
  7. For devices on 25.2 branch: upgrade to 25.2R2 or later (e.g., 25.2R3)
  8. For devices before 23.2: upgrade directly to the minimum fixed version for the target branch (e.g., 23.2R2-S6)
Caveat Standard Junos upgrade precautions apply - test in lab first, ensure configuration backup, plan for FPC reset during upgrade

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
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2026-57019 in production — separate from our analysis above.

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