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When it comes to secure communications, SSL/TLS certificate validation plays a huge role in ensuring data privacy and authenticity. In 2022, Cisco disclosed a major vulnerability — CVE-2022-20814 — that hit its Expressway-C and TelePresence VCS products. This flaw made it easier than ever for attackers to use classic man-in-the-middle (MITM) tricks to snoop or even mess with confidential telecommunication traffic.

This article breaks down how CVE-2022-20814 works, who’s at risk, how attackers can exploit the bug, and what you must do to secure your systems.

What Is CVE-2022-20814?

At its core, this vulnerability is about *insufficient SSL server certificate validation*. Here’s the problem, in plain English:

- Cisco Expressway-C and Cisco TelePresence VCS devices, when connecting to a Cisco Unified Communications Manager (UCM), didn’t properly check if the UCM’s SSL certificate was legit.
- If an attacker got between the devices (think: a MITM position on the network), they could present a fake, self-signed cert and trick Expressway-C or VCS into trusting their rogue server.

Attack Scenario: How Exploitation Works

Imagine an organization’s Cisco Expressway-C is trying to establish a secure connection with its UCM. The attacker, sitting somewhere between those two (for example, via local network, compromised router, or WiFi AP), launches a MITM attack:

Present a Fake Certificate

Instead of forwarding legit UCM’s cert, the attacker presents their *own* (self-signed) SSL certificate.

Lack of Proper Validation

The vulnerable Cisco device *accepts* that certificate without proper validation (doesn’t check if it’s trusted).

Modify or inject messages, potentially leading to further compromise

This entire process can happen *without any credentials*, making it especially dangerous.

Visual: Classic MITM Flow

sequenceDiagram
    participant User
    participant Expressway-C
    participant MITM Attacker
    participant UCM

    User->>Expressway-C: Initiate call setup
    Expressway-C->>MITM Attacker: TLS handshake (thinks it’s UCM)
    MITM Attacker->>Expressway-C: Fake cert (accepted!)
    MITM Attacker->>UCM: TLS handshake
    UCM->>MITM Attacker: Real cert
    MITM Attacker->>UCM: Relay data
    MITM Attacker->>Expressway-C: Decrypt & relay/modify data

*The Expressway-C device accepts the attacker’s certificate, so attacker can view and modify the traffic.*

Exploit Example: Proof-of-Concept

Let’s see a very basic proof-of-concept in Python, where an attacker would use a proxy to catch and strip TLS traffic.

Step 1: Generate a Self-Signed Certificate

openssl req -x509 -newkey rsa:2048 -keyout mitm.key -out mitm.crt -days 365 -nodes -subj "/CN=fake-ucm"

Step 2: MITM Proxy Script (Python)

from mitmproxy import http

def request(flow: http.HTTPFlow) -> None:
    print("Intercepted request: ", flow.request.pretty_url)

def response(flow: http.HTTPFlow) -> None:
    # Here, attacker can read or modify content
    if b'secret' in flow.response.content:
        print("Sensitive data detected!")

An attacker sets up this proxy and configures their network so all Cisco device’s traffic goes through it. Because the device doesn’t validate the cert, it establishes the connection.

*Note: This is simplified for illustration. Real exploits would use more advanced MITM tools like Mitmproxy or Bettercap.*

The ability to impersonate users or redirect calls

This could lead to regulatory or privacy violations for organizations using vulnerable setups.

Not Vulnerable

- Cisco Expressway-E (according to Cisco’s official advisory)

1. Patch Now!

- Cisco has released updated firmware/software that fixes the bug.

- Get latest versions at Cisco’s official download page

- Cisco Software Download

Cisco flatly states: *There are no workarounds*.

- Disabling SSL/TLS, filtering ports, or blocking network access will not mitigate the underlying issue.

Additional References

- Cisco Security Advisory: CVE-2022-20814
- NIST NVD Entry: CVE-2022-20814
- Cisco Unified Communications Manager Security Guide
- Mitmproxy: Tools for MITM testing

Conclusion

CVE-2022-20814 is a reminder that SSL certificate validation isn’t just a checkbox, but a foundational security step. If you’re running old versions of Cisco Expressway-C or TelePresence VCS, you are at risk — and attackers don’t need fancy tricks to break in. If you haven’t patched, now is the time.

Timeline

Published on: 11/15/2024 15:32:47 UTC