# CVE-2026-0203: Junos OS: Receipt of a specifically malformed ICMP packet causes an FPC restart

> An unauthenticated network-adjacent attacker can crash and restart an FPC by sending a malformed ICMPv4 packet, causing a denial of service.

- **Severity:** High 7.1 (`CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/RE:M/U:Amber`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Jan 2026
- **Updated:** 10 Mar 2026
- **Also known as:** GHSA-x6px-8wp8-5cwq

## What is CVE-2026-0203?

CVE-2026-0203 is a high-severity denial of service vulnerability in Juniper Junos, published on 15 Jan 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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.

Weakness: CWE-755 (Improper Handling of Exceptional Conditions)

## Which versions are affected by CVE-2026-0203?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2026-0203?

No fix has been published for CVE-2026-0203 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-0203 being exploited?

There is no known exploitation of CVE-2026-0203 in the wild and no public exploit code.

## Other vulnerabilities in Juniper Junos

- [CVE-2023-36845](https://insights.sbomify.com/CVE-2023-36845/): Juniper Junos OS EX Series and SRX Series PHP External Variable Modification (critical 9.8, exploited in the wild)
- [CVE-2020-1631](https://insights.sbomify.com/CVE-2020-1631/): Juniper Junos OS Path Traversal (high 8.8, exploited in the wild)
- [CVE-2025-21590](https://insights.sbomify.com/CVE-2025-21590/): Juniper Junos OS Improper Isolation or Compartmentalization (medium 6.7, exploited in the wild)
- [CVE-2023-36851](https://insights.sbomify.com/CVE-2023-36851/): Juniper Junos OS SRX Series Missing Authentication for Critical Function (medium 5.3, exploited in the wild)
- [CVE-2023-36844](https://insights.sbomify.com/CVE-2023-36844/): Juniper Junos OS EX Series PHP External Variable Modification (medium 5.3, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-0203 and fix it if it is affected.

What it is: CVE-2026-0203 is a high-severity denial of service vulnerability in Juniper Junos, published on 15 Jan 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-0203 in the wild and no public exploit code.

Affected product: Juniper Junos. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-0203/ (Markdown: https://insights.sbomify.com/CVE-2026-0203/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-0203
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-0203
- OSV: https://osv.dev/vulnerability/CVE-2026-0203

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-0203/
Summaries are generated and may contain mistakes; the official description above is the record.