Cisco Expressway Series and Cisco TelePresence Video Communication Server (VCS) are widely used collaboration solutions that provide secure and efficient video and voice communication. However, the recent discovery of CVE-2022-20809 has highlighted multiple vulnerabilities in these systems that could allow an authenticated, remote attacker to write files or disclose sensitive information on an affected device.

In this long-read post, we will take a deep dive into these vulnerabilities, explore code snippets, and discuss the potential exploits. We will also provide links to original references and updates from Cisco.

Details

CVE-2022-20809 pertains to multiple vulnerabilities found in the API and web-based management interfaces of Cisco Expressway Series and Cisco TelePresence VCS. According to Cisco's official advisory, these vulnerabilities occur due to insufficient input validation and path traversal vulnerabilities in the affected software. An authenticated, remote attacker could exploit these vulnerabilities by sending crafted HTTP requests to a targeted device.

Code Snippet

For illustration purposes, let's consider a hypothetical code snippet that represents the input validation vulnerability:

@app.route('/api/v1/file_upload', methods=['POST'])
def file_upload():
    try:
        uploaded_file = request.files['file']
        filename = request.form['filename']
        # The following line does not validate the user input correctly, 
        # potentially allowing path traversal
        save_path = os.path.join(app.config['UPLOAD_FOLDER'], filename)
        uploaded_file.save(save_path)
        return jsonify(success=True, message='File uploaded successfully'), 200
    except Exception as e:
        return jsonify(success=False, message=str(e)), 500

In the code snippet above, the function file_upload does not validate the filename provided by the user, which could lead to path traversal if a crafted filename were used, resulting in CVE-2022-20809-1.

Exploit Details

An attacker could potentially exploit these vulnerabilities by sending crafted HTTP requests to an affected device. To exploit the path traversal vulnerability (CVE-2022-20809-1), the attacker could send a request similar to the following:

POST /api/v1/file_upload HTTP/1.1
Host: target-device
Content-Type: multipart/form-data; boundary=exampleboundary

--exampleboundary
Content-Disposition: form-data; name="file"; filename="payload.txt"
Content-Type: text/plain

malicious_payload
--exampleboundary
Content-Disposition: form-data; name="filename"

../../etc/payload.txt
--exampleboundary--

In this example, the attacker uses a crafted filename with path traversal sequences (../../etc/payload.txt) to upload a malicious payload to an unintended directory on the targeted device, leading to arbitrary file write (CVE-2022-20809-2) and potentially gaining unauthorized access to sensitive information (CVE-2022-20809-3).

Mitigation and References

To address these vulnerabilities, Cisco has already released software updates. Users are advised to apply these patches as soon as possible. For further information, consult the official Cisco Security Advisory:

- Cisco Expressway Series and TelePresence VCS

As always, ensure that your organization has strong security practices and policies in place, such as proper user access management, network segmentation, and regular monitoring of system logs.

Conclusion

Multiple vulnerabilities in the API and web-based management interfaces of Cisco Expressway Series and Cisco TelePresence Video Communication Server (VCS) could expose users to potential breaches and unauthorized access. Users are urged to update their systems and maintain strong security practices to protect their networks from potential malicious actors.

Timeline

Published on: 05/26/2022 14:15:00 UTC
Last modified on: 06/07/2022 16:36:00 UTC