# CVE-2025-21601: Denial of service in Junos OS

> Unauthenticated attackers can cause a sustained denial of service by sending genuine packets to devices with web management enabled.

- **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/V:C/RE:M/U:Amber`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Apr 2025
- **Updated:** 15 Apr 2025
- **Also known as:** GHSA-95f3-h98w-ww8w

## What is CVE-2025-21601?

CVE-2025-21601 is a high-severity denial of service vulnerability in Juniper Junos, published on 9 Apr 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An Improper Following of Specification by Caller vulnerability in web management (J-Web, Captive Portal, 802.1X, Juniper Secure Connect (JSC) of Juniper Networks Junos OS on SRX Series, EX Series, MX240, MX480, MX960, QFX5120 Series, allows an unauthenticated, network-based attacker, sending genuine traffic targeted to the device to cause the CPU to climb until the device becomes unresponsive. 

Continuous receipt of these packets will create a sustained Denial of Service (DoS) condition.

This issue affects Junos OS: 

  *  All versions before 21.4R3-S9,
  *  from 22.2 before 22.2R3-S5,
  *  from 22.4 before 22.4R3-S4,
  *  from 23.2 before 23.2R2-S3,
  *  from 23.4 before 23.4R2-S3,
  *  from 24.2 before 24.2R1-S1, 24.2R2.

An indicator of compromise is to review the CPU % of the httpd process in the CLI:
e.g.
  show system processes extensive | match httpd  PID nobody       52    0    20M    191M select   2   0:01   80.00% httpd{httpd} <<<<< the percentage of httpd usage if high may be an indicator

Weakness: CWE-573 (Improper Following of Specification by Caller)

## Which versions are affected by CVE-2025-21601?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2025-21601?

No fix has been published for CVE-2025-21601 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-21601 being exploited?

There is no known exploitation of CVE-2025-21601 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-2025-21601 and fix it if it is affected.

What it is: CVE-2025-21601 is a high-severity denial of service vulnerability in Juniper Junos, published on 9 Apr 2025. 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-2025-21601 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-2025-21601/ (Markdown: https://insights.sbomify.com/CVE-2025-21601/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21601
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21601
- OSV: https://osv.dev/vulnerability/CVE-2025-21601

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21601/
Summaries are generated and may contain mistakes; the official description above is the record.