CVE-2018-11714 in TL-WR840N
Summary
by MITRE
An issue was discovered on TP-Link TL-WR840N v5 00000005 0.9.1 3.16 v0001.0 Build 170608 Rel.58696n and TL-WR841N v13 00000013 0.9.1 4.16 v0001.0 Build 170622 Rel.64334n devices. This issue is caused by improper session handling on the /cgi/ folder or a /cgi file. If an attacker sends a header of "Referer: http://192.168.0.1/mainFrame.htm" then no authentication is required for any action.
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Analysis
by VulDB Data Team • 02/14/2020
This vulnerability exists in TP-Link wireless routers TL-WR840N v5 and TL-WR841N v13 firmware versions, representing a critical session management flaw that undermines the device's authentication mechanisms. The issue stems from improper session handling within the web interface's cgi directory, specifically in how the system processes HTTP referer headers during authentication checks. When an attacker crafts a malicious HTTP request containing a specific referer header value of "Referer: http://192.168.0.1/mainFrame.htm", the device bypasses normal authentication procedures and grants unrestricted access to administrative functions. This weakness directly violates the fundamental security principle of proper authentication enforcement and represents a classic example of broken authentication and session management as classified under CWE-613. The vulnerability operates at the application layer and affects the web-based management interface that allows users to configure router settings through standard HTTP protocols.
The technical exploitation of this vulnerability demonstrates a sophisticated bypass mechanism that leverages HTTP header manipulation to circumvent access controls. The attacker does not need valid credentials or session tokens to perform administrative actions on the device, as the system's authentication logic fails to properly validate the request context when the specific referer header is present. This creates a persistent access vector that remains active as long as the device is running and accessible on the network. The flaw essentially allows for privilege escalation without proper authentication, enabling attackers to modify router configurations, change administrator passwords, disable security features, or potentially install malicious firmware. From an operational perspective, this vulnerability transforms any network-connected user into a potential administrator with full control over the device, making it particularly dangerous in environments where routers are exposed to untrusted networks.
The impact of this vulnerability extends beyond simple unauthorized access, as it provides attackers with complete control over the network infrastructure. Once exploited, attackers can modify firewall rules, disable intrusion detection systems, redirect traffic through malicious proxies, or even create backdoors for persistent access. The vulnerability also enables lateral movement within networks where these routers serve as gateways, as compromised devices can be used as entry points to attack other systems. According to ATT&CK framework, this vulnerability maps to T1078 Valid Accounts and T1566 Phishing, as it allows for credential-less access to network infrastructure and can be combined with social engineering to compromise larger network environments. The lack of proper session validation creates a persistent threat vector that can be exploited repeatedly without detection, as the system fails to maintain proper access control states.
Mitigation strategies should focus on immediate firmware updates from TP-Link to address the session handling flaw, as well as network segmentation to isolate critical devices from untrusted networks. Network administrators should implement strict access controls for router management interfaces, ensuring that only authorized personnel can access these systems through secure channels such as VPN connections. Additional protective measures include disabling web management interfaces when not actively needed, implementing network access control lists to restrict access to management ports, and monitoring for suspicious referer headers in network traffic logs. Security professionals should also consider implementing intrusion detection systems that can identify and alert on the specific referer header patterns associated with this vulnerability. The remediation process should include comprehensive network scanning to identify all affected devices, followed by immediate firmware upgrades and security configuration hardening to prevent similar issues in the future. Organizations should also establish regular security assessment procedures to identify and remediate authentication and session management vulnerabilities across their entire network infrastructure.