CVE-2023-20092 - Exploiting Arbitrary File Overwrite in Cisco TelePresence CE and RoomOS
Three critical vulnerabilities—tracked as CVE-2023-20092, CVE-2023-20093, and CVE-2023-20094—were discovered in the CLI interface of Cisco TelePresence CE and RoomOS systems. These vulnerabilities have serious consequences, letting a local attacker with valid credentials overwrite any file on affected devices. In this post, I’ll break down what the flaw is, how exploitation works, and what you should do.
What Is CVE-2023-20092?
CVE-2023-20092 describes a set of bugs in Cisco’s TelePresence and RoomOS systems' command-line interface (CLI). If an attacker already has a remote support user account, they could abuse improper file access controls to place symbolic links (symlinks) in the device’s filesystem. If exploited, this trick causes the system to overwrite files the attacker chooses—even important system files.
Notably: This does not affect Cisco DX70, DX80, TelePresence MX Series, or TelePresence SX Series devices.
Technical Background
The problem comes down to improper access controls and lack of file validation. When certain CLI commands are run, the system may write to files inside predictable directories without checking if those files are actually symlinks.
A legitimate user with shell/CLI access can create a symlink pointing to a file they wish to overwrite. When the system performs regular operations (like logs or configuration saves), it will write to the symlink's destination instead of the intended file.
Step-by-Step Exploit Example
> Disclaimer: This information is for educational purposes only. Do not exploit systems you don’t own.
1. Attacker Connects via Remote Support Account
The attacker needs a valid remote support user account—this isn’t an anonymous exploit.
2. Create a Malicious Symlink
Suppose there’s a file routinely overwritten, say, /tmp/logs/recent.log. The attacker wants to overwrite /etc/shadow (the system’s password file).
# Become the remote support user on the device
cd /tmp/logs
rm -f recent.log
ln -s /etc/shadow recent.log
Now, any time the system attempts to write logs to /tmp/logs/recent.log, it actually writes to /etc/shadow.
3. Trigger the Vulnerable Operation
The attacker either manually triggers a function (if they have enough privileges) or waits for a standard system process (like logging) that writes to recent.log. This could overwrite /etc/shadow with attacker-controlled data, corrupting system base files or even replacing crucial configs or binaries.
> Potential Impact: Device instability, privilege escalation, denial of service, or even gaining root access depending on what files are overwritten.
For official details
- Cisco Security Advisory for CVE-2023-20092
- NIST NVD - CVE-2023-20092
Cisco’s Response and Patches
Cisco released software updates to patch the vulnerabilities. There are no workarounds! The only solution is to upgrade as soon as possible.
Fixed Versions
- CE and RoomOS software updated in June 2023.
How to Patch:
Check your current TelePresence device software version. If it’s not the latest, follow official Cisco upgrade guides or contact support.
Attack Impact: Could corrupt device files, escalate privileges, or brick the device.
Stay safe: Regularly patch your Cisco collaboration devices, disable unnecessary accounts, and audit support credentials.
References:
- Cisco Security Advisory
- NVD CVE-2023-20092
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Timeline
Published on: 11/15/2024 16:15:25 UTC
Last modified on: 11/18/2024 17:11:56 UTC