# CVE-2026-21913: Junos OS: EX4000: A high volume of traffic destined to the device leads to a crash and restart

> An unauthenticated attacker can cause a Juniper EX4000 switch to crash and restart by sending high volumes of traffic, resulting in a service outage.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Jan 2026
- **Updated:** 15 Jan 2026
- **Also known as:** GHSA-p84c-pfqc-c27p

## What is CVE-2026-21913?

CVE-2026-21913 is a high-severity denial of service vulnerability in Juniper Junos, published on 15 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An Incorrect Initialization of Resource vulnerability in the Internal Device Manager (IDM) of Juniper Networks Junos OS on EX4000 models allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).

On EX4000 models with 48 ports (EX4000-48T, EX4000-48P, EX4000-48MP) a high volume of traffic destined to the device will cause an FXPC crash and restart, which leads to a complete service outage until the device has automatically restarted.

The following reboot reason can be seen in the output of 'show chassis routing-engine' and as a log message:

  reason=0x4000002 reason_string=0x4000002:watchdog + panic with core dump 

This issue affects Junos OS on EX4000-48T, EX4000-48P and EX4000-48MP:

  *  24.4 versions before 24.4R2,
  *  25.2 versions before 25.2R1-S2, 25.2R2.

This issue does not affect versions before 24.4R1 as the first Junos OS version for the EX4000 models was 24.4R1.

Weakness: CWE-665 (Improper Initialization), CWE-1419 (Incorrect Initialization of Resource)

## Which versions are affected by CVE-2026-21913?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2026-21913?

No fix has been published for CVE-2026-21913 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-21913 being exploited?

There is no known exploitation of CVE-2026-21913 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-2026-21913 and fix it if it is affected.

What it is: CVE-2026-21913 is a high-severity denial of service vulnerability in Juniper Junos, published on 15 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-21913 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-2026-21913/ (Markdown: https://insights.sbomify.com/CVE-2026-21913/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21913
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21913
- OSV: https://osv.dev/vulnerability/CVE-2026-21913

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-21913/
Summaries are generated and may contain mistakes; the official description above is the record.