CVE-2023-20091 - Exploiting Cisco TelePresence CE and RoomOS Arbitrary File Overwrite Vulnerability

In March 2023, Cisco disclosed a significant vulnerability, CVE-2023-20091, affecting their TelePresence CE and RoomOS software. This flaw allows an authenticated local attacker to overwrite important files on the affected device’s file system—potentially leading to a full system compromise. This post explains the root cause behind this vulnerability, illustrates how attackers can leverage it, and provides real-world guidance for mitigation.

What’s The Problem?

CVE-2023-20091 exists due to improper access controls on certain files in the local file system of Cisco TelePresence CE and RoomOS products. This improper control allows a local support user—not just administrators—to manipulate and overwrite files by exploiting symbolic links (symlinks).

Simply put: Once an attacker gets support-level access (which isn’t as strong as admin), they can trick the system into replacing any file they target.

Cisco RoomOS Software

are at risk—find the official affected product list and patched versions at Cisco’s advisory.

Planting a Symlink:

The attacker creates a symbolic link (symlink) at a specific spot on the filesystem that points to ANY file they want to overwrite.

Triggering File Operations:

When the system tries to write to the symlink location thinking it’s a safe file, it actually writes to wherever the symlink points. This can lead to corruption or even escalation of privileges!

Here’s what this looks like in action

# Assume the attacker is logged in as a support user on the TelePresence/RoomOS device

# Suppose there's a maintenance file '/tmp/diag_upload' 
# The attacker wants to overwrite '/etc/shadow' (the system password file)

cd /tmp

# Create a malicious symlink named 'diag_upload' that points to '/etc/shadow'
ln -s /etc/shadow diag_upload

# When a privileged process writes to 'diag_upload', 
# it unknowingly overwrites /etc/shadow instead!

Warning: Overwriting /etc/shadow could lock out users, escalate privileges, or even “brick” the device.

Real-World Attack Scenario

Let’s make it simple:
Imagine a helpdesk technician has support account access for troubleshooting a TelePresence device. If this individual is a malicious insider, or if their account was compromised, they could drop symlinks and sabotage or take over the system—without needing full admin rights.

Remote support account (not just public or guest access)

- Local access (either physically or via SSH/console)

Why Is This Dangerous?

- Overwrite Security Files: Attackers can target sensitive files (like /etc/passwd, /etc/shadow, device configuration files).

Persistence: Gain persistence by adding themselves as root users.

- Brick Devices: By overwriting critical firmware/config files, the box could become unusable, leading to downtime.

Original References

- Cisco Security Advisory: Arbitrary File Write Vulnerability in TelePresence CE and RoomOS (CVE-2023-20091)
- NVD Entry: CVE-2023-20091

Is There A Fix?

Yes: Cisco has released security updates for both affected platforms.

- Update immediately to the latest safe versions.
- No workarounds: If you can’t update, the only mitigation is to restrict and monitor remote support account access.

Monitor logs: Unusual symlink creation could be a red flag.

Cisco says: “There are no workarounds that address this vulnerability.”

Conclusion

CVE-2023-20091 shows that even lower-privilege accounts can become extremely dangerous if file system permissions aren’t handled securely. If you use Cisco TelePresence or RoomOS, check your version and patch immediately.

Timeline

Published on: 11/15/2024 16:15:25 UTC