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JunosOperating system · Juniper

CVE-2026-0203

MEDIUM · 6.5 CVSS v3.1 Published 2026-01-15
Fix available
A fix is available. Upgrade to 21.2 or later.
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 Handling of Exceptional Conditions vulnerability in packet processing of Juniper Networks Junos OS allows an unauthenticated, network-adjacent attacker sending a specifically malformed ICMP packet to cause an FPC to crash and restart, resulting in a Denial of Service (DoS). When an ICMP packet is received with a specifically malformed IP header value, the FPC receiving the packet crashes and restarts. Due to the specific type of malformed packet, adjacent upstream routers would not forward the packet, limiting the attack surface to adjacent networks. This issue only affects ICMPv4. ICMPv6 is not vulnerable to this issue. This issue does not affect AFT-based line cards such as the MPC10, MPC11, LC4800, LC9600, and MX304. This issue affects Junos OS:  * all versions before 21.2R3-S9,  * from 21.4 before 21.4R3-S10,  * from 22.2 before 22.2R3-S7,  * from 22.3 before 22.3R3-S4,  * from 22.4 before 22.4R3-S5,  * from 23.2 before 23.2R2-S3,  * from 23.4 before 23.4R2-S3,  * from 24.2 before 24.2R1-S2, 24.2R2.

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

A vulnerability in Junos OS packet processing allows an unauthenticated, network-adjacent attacker to send a specifically malformed ICMPv4 packet with an invalid IP header value, causing the FPC (Forwarding Packet Processor) to crash and restart, resulting in denial of service. ICMPv6 and AFT-based line cards are not affected.

MitigationApply the appropriate Junos OS software update (21.2R3-S9, 21.4R3-S10, 22.2R3-S7, 22.3R3-S4, 22.4R3-S5, 23.2R2-S3, 23.4R2-S3, or 24.2R1-S2/24.2R2) to all affected devices. If immediate patching is not feasible, consider network segmentation to limit exposure to adjacent networks only.

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:< 21.2= 21.2= 21.4= 22.2= 22.3= 22.4= 23.2= 23.4= 24.2

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. Identify Junos OS version
    Run 'show version' or 'show version detail' on the device to obtain the installed Junos OS version
    Affected if The displayed version matches any of these: < 21.2, 21.2, 21.4, 22.2, 22.3, 22.4, 23.2, 23.4, or 24.2 (note: 24.2R1-S1 and earlier 24.2 versions are affected; only 24.2R1-S2 or 24.2R2 and later are fixed)
  2. Confirm ICMPv4 processing is enabled
    Verify that the device processes ICMPv4 traffic. This is typically enabled by default. Use 'show icmp' or check firewall filter configurations that may permit ICMPv4
    Affected if ICMPv4 processing is active on any interface reachable from adjacent network segments
  3. Identify FPC line cards
    Run 'show chassis fpc' to list Forwarding Packet Cards installed in the device
    Affected if The device has one or more FPCs (non-AFT based line cards) present; AFT-based line cards are not affected according to the CVE
  4. Check for recent FPC restarts
    Run 'show chassis fpc' and review the 'Uptime' field for any FPCs with very short uptime, or use 'show log messages' searching for FPC crash indicators
    Affected if Any FPC shows recent restarts or crash-related messages in the system logs

You are affected if the device runs any Junos OS version listed as vulnerable AND has ICMPv4 reachable FPC line cards (non-AFT based) that could process malformed ICMPv4 packets from adjacent networks.

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 21.2 or later
Fixed in 21.2
Interim mitigation

Apply the appropriate Junos OS software update (21.2R3-S9, 21.4R3-S10, 22.2R3-S7, 22.3R3-S4, 22.4R3-S5, 23.2R2-S3, 23.4R2-S3, or 24.2R1-S2/24.2R2) to all affected devices. If immediate patching is not feasible, consider network segmentation to limit exposure to adjacent networks only.

Recommended fix High confidence

21.2R3-S9, 21.4R3-S10, 22.2R3-S7, 22.3R3-S4, 22.4R3-S5, 23.2R2-S3, 23.4R2-S3, or 24.2R2 (depending on current branch)

  1. Identify the current Junos OS version running on the device using 'show version' command
  2. Determine which version branch your current release belongs to (21.2.x, 21.4.x, 22.2.x, 22.3.x, 22.4.x, 23.2.x, 23.4.x, or 24.2.x)
  3. Download the appropriate fixed release for your branch from the Juniper Networks support portal
  4. Upgrade the device to the fixed version using 'request system software add' command with the appropriate package
  5. Reboot the device after upgrade completes using 'request system reboot' command
  6. Verify the new version is running with 'show version' and confirm FPCs are online with 'show chassis fpc'
Caveat Review Juniper release notes for your target version for any known compatibility issues or configuration changes; test upgrade in lab environment first

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

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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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-2026-0203 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
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