CVE-2023-20094 - How a Bounds Check Flaw Exposes Sensitive Data in Cisco Webex Desk Hub

In June 2023, Cisco disclosed CVE-2023-20094, a vulnerability which affects certain TelePresence CE and RoomOS products, notably the Cisco Webex Desk Hub. This bug lets a local or adjacent attacker view sensitive information on otherwise protected devices. In this post, I’ll break down how the flaw works, give you simplified code snippets, and explain how an attacker could exploit it. Let’s dig in!

What Is CVE-2023-20094?

The vulnerability is a classic _out-of-bounds read_ (OOB Read), which happens when software doesn’t check the boundaries (size and end-points) of memory buffers properly. Specifically, the affected Cisco software reads data beyond what it’s supposed to, which can leak details that should be kept private—like fragments of other users' information, configuration settings, or even authentication material.

Impacted product: _Cisco Webex Desk Hub, running vulnerable versions of TelePresence CE or RoomOS._
Not impacted: Other TelePresence or RoomOS gear.
Who can exploit: Adjacent attackers only—that is, attackers who can access the same layer 2 network segment as the Desk Hub (such as on the same Wi-Fi or wired LAN).

How the Flaw Exists

In vulnerable versions, the Desk Hub processes certain requests from the network without proper "bounds checking." Simply put, it fails to make sure the data it reads is within valid memory locations.

According to Cisco’s advisory (CVE-2023-20094 - Security Advisory), the root of the problem is:

> "A vulnerability in the handling of certain requests could allow an unauthenticated, adjacent attacker to read sensitive information from memory."

Let’s see a simplified example of what this kind of bug looks like in code

// Pseudo-code to illustrate the faulty pattern

char buffer[256];
int len = get_request_length(); // The length comes from attacker input!

// BAD: No validation of len! Should always make sure len <= sizeof(buffer)
memcpy(buffer, input, len);

// Later, buffer content is sent in response, up to len bytes.
// If len exceeds buffer, that memory can come from elsewhere: OOB READ!

If len is too large, the Desk Hub ends up reading from memory locations next to buffer, which may contain sensitive data left by other users, processes, or the underlying system itself.

Exploitation Details: How An Attacker Does It

An attacker must be on the same network segment as the Desk Hub device. Here’s the general exploitation flow:

1. Craft a malicious network request: The attacker sends a specially crafted packet or request to the Desk Hub.
2. Trigger the OOB Read: The request includes a length field (or another parameter) that is larger than the internal buffer the Desk Hub uses.
3. Receive the leaked data: The Desk Hub responds, echoing back not just the right data, but also trailing memory from its own process.

Here’s a high-level Python exploit snippet (conceptual, not an actual working exploit) that demonstrates this idea:

import socket

# Desk Hub's IP and relevant port
TARGET_IP = '192.168.1.100'
TARGET_PORT = 12345  # (Replace with real port used by Desk Hub protocol)

# Craft an overlong request with a huge 'length'
payload = b'\x00' + b'A' * 300  # 300 bytes, buffer is only 256!

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((TARGET_IP, TARGET_PORT))

sock.sendall(payload)
reply = sock.recv(512)

# The reply may include extra data from memory adjacent to the buffer
print("Leaked response:", reply)

Note: The actual protocol or trigger for this bug is proprietary to Cisco. The above is only a general demonstration of how OOB Reads typically get exploited.

OAuth or API tokens, depending on what’s in memory at the time

Essentially, any confidential data lingering in memory is at risk.

Fixes & Workarounds

There are no workarounds.
Mitigation relies solely on Cisco-issued firmware/security updates. Cisco has released patched software for all affected products.

- Cisco download portal
- Cisco Security Advisory page with fixed versions

If you use Cisco Webex Desk Hub, you should update it as soon as possible.
If patching is not immediately possible, segment the device from untrusted local networks and enable network access controls.

Conclusion

CVE-2023-20094 is a classic case where overlooking proper bounds checking can cause serious real-world data leaks, even for expensive enterprise equipment like Cisco’s Webex Desk Hub. If you’re in IT and managing these devices, make firmware updating a top priority.

Timeline

Published on: 11/15/2024 15:08:04 UTC
Last modified on: 11/15/2024 15:08:14 UTC