CVE-2025-1976 - Privilege Escalation in Brocade Fabric OS 9.1.

CVE-2025-1976 is a critical local privilege escalation vulnerability affecting Brocade Fabric OS, a widely used storage networking platform. Starting with version 9.1., Brocade Fabric OS removed direct root shell access for security. However, versions 9.1. through 9.1.1d6 remain vulnerable—an authenticated user with admin privileges can run code as root.

This post explains how the vulnerability works, provides a proof-of-concept code snippet, and offers mitigation guidance. Exploitability means anyone with admin credentials could fully compromise a switch.

Vulnerability: Admin user can run arbitrary code as root (local privilege escalation)

- Root Cause: Unsafe service/script runs as root but is accessible to admins

References:

- Brocade Security Advisory (Example)
- NIST CVE Record (once published)

Background

Brocade Fabric OS is used in SANs (Storage Area Networks) worldwide. In legacy versions, the root account gave direct access, but from 9.1. forward, root logins were removed for better security. Instead, admin users log in with restricted privileges.

But some system scripts and services *still* run as root on the backend. If one of these can be influenced by an admin, it can lead to privilege escalation.

Vulnerability Details

An internal maintenance or log management script, commonly present in enterprise appliances, might be world-readable or modifiable by the admin user, or its input might be drawn from a location admin can write to. Brocade Fabric OS runs some of these scripts as root periodically or via the restricted shell.

If the script, for example /etc/cron.daily/fos_maintenance, reads files from /var/admin/, then an admin can put a malicious file there. If the script loads code or commands from that file, the code runs as root. This is called *insecure file inclusion* or *insecure script execution*.

Attacker logs in as admin via SSH or the console.

- Attacker drops a malicious payload in a location the admin can write to (e.g., /var/admin/myroot.sh).
- The maintenance script, run as root (either immediately or on a schedule), picks up attacker’s file and executes it unrestricted.

Proof-of-Concept Exploit (Hypothetical Example)

Suppose /var/admin/hooks/startup.sh is executed by a root-owned startup service. Although, by default, only root should write to this file, suppose faulty permissions let admin users edit it:

# On the switch as 'admin' user
echo "cp /bin/sh /var/tmp/rootsh; chmod 4755 /var/tmp/rootsh" >> /var/admin/hooks/startup.sh

In this command, we append a line that copies the shell and gives it setuid (root) permissions.

After the maintenance script runs (by reboot or schedule)

# Back on the switch as admin
/var/tmp/rootsh
id

Output

uid=(root) gid=(root) groups=(root)

The admin user has root privileges. Game over.

Note: This code is for educational purposes. Do not use it against any system you do not own or have permission to test.

Mitigation Guidance

- Upgrade: Brocade/ Broadcom has patched this issue starting in Fabric OS 9.1.1d7. Update your switches immediately.

Audit: Check file permissions for scripts and directories writable by non-root users.

- Monitor: Regularly check your devices for unexpected files or elevated SUID binaries in places like /var/tmp/.

For latest updates

- Official Security Advisories
- Recommended Security Practices Whitepaper

References

- Brocade Fabric OS Downloads & Notes
- CVE-2025-1976 at NVD (once available)
- Linux Privilege Escalation Fundamentals

Final Thoughts

Even in devices designed for security, unsafe default permissions or forgotten scripts can turn admin users into root users with disastrous potential. Always apply firmware updates promptly and regularly audit internal scripts and access permissions. This vulnerability reinforces the need for 'defense in depth' even after root logins are "removed."

Timeline

Published on: 04/24/2025 03:15:14 UTC
Last modified on: 04/29/2025 19:49:59 UTC