CVE-2020-27403: TCL Smart TV Information Disclosure Flaw

CVE-2020-27403 Overview

CVE-2020-27403 is an information disclosure vulnerability affecting TCL Android Smart TV series manufactured by TCL Technology Group Corporation. The vulnerability exists in an insecure web server running on port 7989 that exposes a directory listing of all files and directories on the device. An attacker on the adjacent network can arbitrarily browse and download sensitive files from affected devices without authentication.

The vulnerability is particularly concerning because it allows unprivileged remote attackers to download critical system files, leading to serious information disclosure. Additionally, some TV models and firmware versions may expose the webserver on additional ports (such as port 7983 discovered on the U43P6046 model running Android 8.0) with the entire filesystem accessible. The webserver is also bound to the localhost interface, making it accessible to all unprivileged installed apps on the Android system, including regular web browsers. This means any malicious app can read files from other apps, including Android system settings, saved passwords, and private keys.

Critical Impact

Adjacent network attackers and local unprivileged apps can access sensitive system files including credentials, private keys, and configuration data from TCL Smart TVs.

Affected Products

• TCL 32S330 and 32S330 Firmware
• TCL 40S330 and 40S330 Firmware
• TCL 43S434 and 43S434 Firmware
• TCL 50S434 and 50S434 Firmware
• TCL 55S434 and 55S434 Firmware
• TCL 65S434 and 65S434 Firmware
• TCL 75S434 and 75S434 Firmware
• TCL V8-R851T02-LF1 V295 and below
• TCL V8-T658T01-LF1 V373 and below

Discovery Timeline

• 2020-11-10 - CVE-2020-27403 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-27403

Vulnerability Analysis

This vulnerability is classified as CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). The affected TCL Android Smart TVs run an insecure web server that provides directory listing functionality without any authentication or access controls. The web server, accessible on port 7989 by default, presents a complete view of the device's file system to any user on the adjacent network.

The impact extends beyond simple network-based attacks. Since the webserver is bound to the localhost interface, any application installed on the TV—regardless of its privilege level—can access the entire filesystem through standard HTTP requests. This effectively bypasses Android's application sandboxing and permission model, allowing malicious apps to harvest sensitive data from other applications and system components.

Root Cause

The root cause of this vulnerability is the implementation of a web server service on TCL Android Smart TVs that lacks fundamental security controls. The server was deployed without authentication mechanisms, access control lists, or proper network binding restrictions. By exposing a directory listing of the entire filesystem and binding to interfaces accessible from both the local network and localhost, the design fundamentally violates the principle of least privilege and exposes sensitive system resources to unauthorized access.

Attack Vector

The attack can be executed from two vectors. First, an attacker positioned on the adjacent network (same Wi-Fi or local network segment) can directly connect to port 7989 (or port 7983 on some models) and browse the filesystem using any web browser or HTTP client. Second, a malicious Android application installed on the TV can make local HTTP requests to the webserver, extracting sensitive files without requiring any special permissions.

An attacker exploiting this vulnerability could retrieve system configuration files, stored credentials, private cryptographic keys, cached application data, and other sensitive information stored on the device. The attack requires no user interaction and can be automated for mass exploitation across vulnerable devices on the same network segment.

Detection Methods for CVE-2020-27403

Indicators of Compromise

• Unexpected HTTP connections to ports 7989 or 7983 on TCL Smart TV devices
• Network traffic showing directory listing requests or bulk file downloads from Smart TV IP addresses
• Suspicious applications on the TV making localhost HTTP requests to the vulnerable ports
• Log entries indicating external access to sensitive system files via the web server

Detection Strategies

• Monitor network traffic for HTTP connections to unusual ports (7989, 7983) targeting Smart TV devices on the network
• Implement network segmentation to isolate IoT devices and monitor cross-segment traffic for anomalies
• Deploy intrusion detection rules to alert on directory traversal patterns or bulk file downloads from Smart TV devices
• Conduct periodic network scans to identify exposed services on IoT devices within the enterprise environment

Monitoring Recommendations

• Configure network monitoring tools to alert on any connections to known vulnerable ports on TCL Smart TV devices
• Review Smart TV application installations for potentially malicious apps that could exploit local access
• Implement logging at network boundaries to capture traffic patterns involving IoT devices
• Periodically audit Smart TV firmware versions against known vulnerable versions

How to Mitigate CVE-2020-27403

Immediate Actions Required

• Isolate affected TCL Smart TV devices on a separate network segment with restricted access
• Block inbound connections to ports 7989 and 7983 on TCL Smart TVs using firewall rules
• Audit installed applications on affected devices and remove any untrusted or unnecessary apps
• Check for and apply any available firmware updates from TCL

Patch Information

TCL has acknowledged the vulnerability and provided guidance through their support portal. Users should consult the TCL Support Advisory on Vulnerabilities for the latest firmware updates and security patches. It is critical to update affected devices to the latest available firmware version that addresses this vulnerability.

For detailed technical information about the vulnerability, refer to the GitHub Security Advisory SICK-2020-009 and the Sick Codes Analysis on TCL Vulnerabilities.

Workarounds

• Place TCL Smart TVs on an isolated IoT network segment without direct access to sensitive network resources
• Implement firewall rules to block external access to ports 7989 and 7983 on Smart TV devices
• Restrict application installations on the TV to only trusted sources and essential applications
• Consider disabling network connectivity on affected TVs when not actively required for streaming services

# Example firewall rule to block access to vulnerable ports (iptables)
iptables -A INPUT -p tcp --dport 7989 -j DROP
iptables -A INPUT -p tcp --dport 7983 -j DROP

# Example network segmentation using VLAN tagging
# Place IoT devices including Smart TVs on a dedicated VLAN
# Configure inter-VLAN routing to restrict access to sensitive resources