CVE-2026-51735 in TOTOLINK
Summary
by MITRE • 08/31/2026
Incorrect access control in the showSyslog function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to retrieve recent system logs via sending a crafted POST request to /cgi-bin/cstecgi.cgi.
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Analysis
by VulDB Data Team • 08/31/2026
The vulnerability identified in the showSyslog function of TOTOLINK T6 router firmware version 4.1.5cu.748_B20211015 represents a critical failure in access control mechanisms within the device's web management interface. This flaw specifically affects the endpoint located at /cgi-bin/cstecgi.cgi, which is responsible for handling various administrative tasks including system log retrieval. The core technical issue lies in the insufficient validation of authentication tokens or session states when processing POST requests directed to this specific function. Consequently, an attacker who does not possess valid administrator credentials can interact with this endpoint directly by crafting a malicious HTTP POST request that mimics legitimate administrative traffic. This bypasses the intended security controls designed to restrict access to sensitive system information solely to authenticated users.
From a technical perspective, the vulnerability stems from a lack of proper authorization checks within the server-side logic handling the showSyslog operation. In secure implementations, any attempt to retrieve syslog data should require verification that the requesting user has an active, valid session with appropriate privileges. However, in this affected firmware version, the application fails to enforce these constraints effectively. An unauthenticated actor can exploit this by sending a specifically crafted POST request containing parameters that trigger the log retrieval process without prior authentication. This type of flaw is characteristic of broken access control vulnerabilities where the server trusts client-side inputs or session identifiers too implicitly without rigorous backend verification against an authorized user database or token store.
The operational impact of this vulnerability is significant, as it allows for the exfiltration of recent system logs which often contain sensitive diagnostic information. These logs may reveal internal network topology details such as IP addresses of connected devices, gateway configurations, and potentially previously logged error messages that could hint at other security weaknesses or misconfigurations within the local network environment. Furthermore, syslog data might include timestamps and event descriptions related to login attempts, configuration changes, or system errors that can aid an attacker in planning further exploitation steps against the router or downstream devices on the same subnet. This information disclosure undermines the confidentiality of the network infrastructure and reduces the barrier for subsequent attacks such as privilege escalation or lateral movement within a local area network.
This vulnerability aligns with CWE-284, which describes Improper Access Control, specifically where access control decisions are not performed correctly by an authoritative actor. Additionally, it maps to MITRE ATT&CK technique T1078, Valid Accounts, although in this case the attacker is unauthenticated but exploits a flaw that effectively grants them unauthorized valid-like access to restricted resources. The exploitation vector falls under Remote Code Execution or Information Disclosure via Network protocols, specifically leveraging HTTP POST methods which are often less scrutinized than GET requests by basic security monitoring tools if not properly configured with deep packet inspection capabilities.
To mitigate this risk, users of the TOTOLINK T6 router should immediately update their firmware to a patched version that addresses these access control deficiencies in the showSyslog function and related CGI endpoints. If an immediate patch is unavailable, administrators can implement network-level controls such as firewall rules or Access Control Lists (ACLs) to restrict access to /cgi-bin/cstecgi.cgi exclusively from trusted management IP addresses. Additionally, disabling remote administration features if not strictly necessary reduces the attack surface exposed to external networks. Regular monitoring of router logs for unusual POST requests targeting CGI binaries can also help in detecting potential exploitation attempts before significant data exfiltration occurs.