CVE-2020-35575: TP-Link WA901ND Auth Bypass Vulnerability

CVE-2020-35575 Overview

A password-disclosure vulnerability exists in the web interface on certain TP-Link devices that allows a remote attacker to obtain full administrative access to the web panel. This vulnerability affects a wide range of TP-Link consumer and small office/home office (SOHO) routers and access points, making it a significant security concern for network infrastructure.

Critical Impact

Remote attackers can gain full administrative control over affected TP-Link devices without authentication, potentially compromising the entire network infrastructure, modifying configurations, intercepting traffic, or using the device as a pivot point for further attacks.

Affected Products

• TP-Link WA901ND (firmware before 3.16.9(201211) beta)
• TP-Link Archer C5 and Archer C7
• TP-Link MR3420 and MR6400
• TP-Link WA701ND and WA801ND
• TP-Link WDR3500 and WDR3600
• TP-Link WE843N
• TP-Link WR1043ND and WR1045ND
• TP-Link WR740N, WR741ND, WR749N
• TP-Link WR802N, WR840N, WR841HP, WR841N
• TP-Link WR842N, WR842ND, WR845N
• TP-Link WR940N, WR941HP, WR945N, WR949N
• TP-Link WRD4300

Discovery Timeline

• December 26, 2020 - CVE-2020-35575 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-35575

Vulnerability Analysis

This vulnerability resides in the web management interface of numerous TP-Link router models. The flaw allows unauthenticated remote attackers to extract administrative credentials directly from the device's web interface. Once obtained, these credentials grant complete administrative control over the router, enabling attackers to modify network configurations, alter DNS settings, update firmware with malicious versions, or establish persistent backdoor access.

The vulnerability is particularly dangerous because it requires no user interaction and can be exploited remotely over the network. Devices exposed directly to the internet or accessible within a compromised network segment are at immediate risk. The affected product line spans multiple generations of TP-Link hardware, indicating a systemic issue in the firmware's credential handling mechanisms.

Root Cause

The vulnerability stems from improper protection of administrative credentials within the web interface. The device firmware fails to adequately secure the password information, allowing it to be accessed or extracted through the web management interface without proper authentication checks. This represents a fundamental failure in secure credential storage and access control implementation.

Attack Vector

The attack can be executed remotely over the network by any attacker who can reach the device's web interface. The exploitation requires no privileges, no user interaction, and presents low complexity for attackers. An adversary would target the web management interface, typically accessible on port 80 or 443, and leverage the password disclosure flaw to retrieve administrative credentials.

Once credentials are obtained, the attacker gains the same level of access as the legitimate administrator. This includes the ability to modify wireless settings, change DNS servers to redirect traffic, update firmware, access connected device information, and potentially pivot to attack other devices on the network.

Detection Methods for CVE-2020-35575

Indicators of Compromise

• Unexpected administrative login attempts or successful logins from unknown IP addresses in router logs
• Configuration changes to DNS settings, wireless parameters, or remote management options without administrator action
• Unusual outbound traffic patterns from the router indicating potential command-and-control communication
• Firmware version changes or unexpected reboots of the affected device

Detection Strategies

• Monitor network traffic for unusual access patterns to router management interfaces (ports 80/443)
• Implement network intrusion detection rules to identify exploitation attempts targeting TP-Link web interfaces
• Regularly audit router configurations and compare against known-good baselines to detect unauthorized changes
• Review authentication logs for evidence of credential extraction or unauthorized administrative access

Monitoring Recommendations

• Enable logging on affected devices and forward logs to a central SIEM for analysis
• Set up alerts for administrative access from unexpected source IP addresses
• Monitor for DNS configuration changes that could indicate attacker manipulation
• Implement network segmentation to limit exposure of management interfaces and track cross-segment access attempts

How to Mitigate CVE-2020-35575

Immediate Actions Required

• Update affected TP-Link devices to the latest firmware version immediately; for WA901ND, version 3.16.9(201211) or later
• Disable remote management access from WAN interfaces to prevent external exploitation
• Change default administrative credentials and use strong, unique passwords for each device
• Restrict access to the router's web management interface to trusted IP addresses only
• Consider placing critical network infrastructure behind a firewall or VPN

Patch Information

TP-Link has released firmware updates to address this vulnerability. For the WA901ND, firmware version 3.16.9(201211) beta or later resolves the issue. Users should visit the TP-Link Security Resources page to find the appropriate firmware updates for their specific device models. The TP-Link Firmware Update for WA901ND is available for download.

Workarounds

• Disable remote management entirely if firmware updates are not immediately available
• Implement network-level access controls to restrict management interface access to specific administrator workstations
• Use a separate, isolated management VLAN for router administration to limit exposure
• Monitor the device for signs of compromise and be prepared to factory reset and reconfigure if suspicious activity is detected

# Network-level mitigation using firewall rules (example for Linux iptables)
# Block external access to router management interface
iptables -A FORWARD -p tcp --dport 80 -d ROUTER_IP -j DROP
iptables -A FORWARD -p tcp --dport 443 -d ROUTER_IP -j DROP

# Allow only trusted admin workstation
iptables -I FORWARD -p tcp --dport 80 -s ADMIN_IP -d ROUTER_IP -j ACCEPT
iptables -I FORWARD -p tcp --dport 443 -s ADMIN_IP -d ROUTER_IP -j ACCEPT