CVE-2021-21332

Synapse Matrix server XSS vulnerability (fixed in 1.27.0)

• CVSS 8.2
• CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
• Configuration Issues
• Remote

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains. This is fixed in version 1.27.0.

CVE

CVE-2021-21332

CWE

CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CVSS base score

8.2

Published

2021-03-26

OWASP

A05 Security Misconfiguration

Orthogonal defect classification

Function

Code defect classification

Incorrect Functionality

Category

Configuration Issues

Subcategory

Cross-Site Scripting (XSS)

Accessibility scope

Remote

Impact

Information Disclosure

Fixed by upgrading

Yes

Solution

Update to Synapse version 1.27.0 or higher.

from flask import Flask, request, render_template_string

app = Flask(__name__)

@app.route('/reset_password', methods=['GET', 'POST'])
def reset_password():
    if request.method == 'POST':
        user_input = request.form['user_input']
        return f"Password reset link has been sent to {user_input}"
    
    return render_template_string('''
        <form method="post">
            <label for="user_input">Enter your email:</label>
            <input type="text" id="user_input" name="user_input">
            <input type="submit" value="Reset Password">
        </form>
    ''')

if __name__ == '__main__':
    app.run()

from flask import Flask, request, render_template_string
import html

app = Flask(__name__)

@app.route('/reset_password', methods=['GET', 'POST'])
def reset_password():
    if request.method == 'POST':
        user_input = request.form['user_input']
        sanitized_input = html.escape(user_input)
        return f"Password reset link has been sent to {sanitized_input}"
    
    return render_template_string('''
        <form method="post">
            <label for="user_input">Enter your email:</label>
            <input type="text" id="user_input" name="user_input">
            <input type="submit" value="Reset Password">
        </form>
    ''')

if __name__ == '__main__':
    app.run()

@misc{vaitp:cve202121332,
  title        = {{Synapse Matrix server XSS vulnerability (fixed in 1.27.0)}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2021},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2021-21332},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2021-21332/}}
}