# CVE-2025-21591: Junos OS: An unauthenticated adjacent attacker sending a malformed DHCP packet causes jdhcpd to crash

> An unauthenticated adjacent attacker can crash the jdhcpd daemon by sending malformed DHCP packets when DHCP snooping is enabled, 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:U/V:C/RE:M/U:Green`)
- **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:** 9 Apr 2025
- **Updated:** 28 Apr 2025
- **Also known as:** GHSA-6pgh-5wh4-5pph

## What is CVE-2025-21591?

CVE-2025-21591 is a high-severity denial of service vulnerability in Juniper Junos, published on 9 Apr 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A Buffer Access with Incorrect Length Value vulnerability in the jdhcpd daemon of Juniper Networks Junos OS, when DHCP snooping is enabled, allows an unauthenticated, adjacent, attacker to send a DHCP packet with a malformed DHCP option to cause jdhcp to crash creating a Denial of Service (DoS) condition.

Continuous receipt of these DHCP packets using the malformed DHCP Option will create a sustained Denial of Service (DoS) condition.

This issue affects Junos OS:

  *  from 23.1 before 23.2R2-S3,
  *  from 23.4 before 23.4R2-S3,
  *  from 24.2 before 24.2R2.

This issue isn't applicable to any versions of Junos OS before 23.1R1. 

This issue doesn't affect vSRX Series which doesn't support DHCP Snooping. 

This issue doesn't affect Junos OS Evolved.

There are no indicators of compromise for this issue.

Weakness: CWE-805 (Buffer Access with Incorrect Length Value)

## Which versions are affected by CVE-2025-21591?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2025-21591?

No fix has been published for CVE-2025-21591 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-21591 being exploited?

There is no known exploitation of CVE-2025-21591 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-2025-21591 and fix it if it is affected.

What it is: CVE-2025-21591 is a high-severity denial of service vulnerability in Juniper Junos, published on 9 Apr 2025. 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-2025-21591 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-2025-21591/ (Markdown: https://insights.sbomify.com/CVE-2025-21591/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21591
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21591
- OSV: https://osv.dev/vulnerability/CVE-2025-21591

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21591/
Summaries are generated and may contain mistakes; the official description above is the record.