Description

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.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.5",
  "pubDate": "2026-08-31T20:17:04.773Z",
  "pubdate": "2026-08-31T20:17:04.773Z",
  "executiveSummary": "The TOTOLINK T6, specifically version 4.1.5cu.748_B20211015, contains an improper access control vulnerability within its web management interface.\nThe flaw allows unauthenticated remote attackers to bypass authorization mechanisms and retrieve sensitive system logs.\nThe vulnerability resides in the showSyslog function, reachable via the cstecgi.cgi gateway.\nSuccessful exploitation results in the unauthorized disclosure of diagnostic data, which may contain sensitive information such as network configuration, device state, or activity metadata.\nThis vulnerability is critical as it requires zero authentication, enabling remote adversaries to conduct reconnaissance against the device without needing valid administrative credentials.\nThe risk implication involves a total breakdown of management interface access controls, potentially aiding further exploitation or identifying internal network topology.",
  "technicalDetails": "The vulnerability is localized within the /cgi-bin/cstecgi.cgi script, which acts as a central dispatcher for various backend management functions on the TOTOLINK T6 device.\nThe root cause is an insecure implementation of access control checks within the showSyslog function. In a secure firmware design, functions that expose sensitive system state or diagnostic information are wrapped in an authentication middleware layer that validates session tokens or cookies.\nIn this specific instance, the showSyslog function fails to perform a verification check to ensure the requester possesses an active, authorized administrative session before processing the request.\nThe attack flow begins when an attacker sends a specially crafted POST request directed at /cgi-bin/cstecgi.cgi. By manipulating the request body or associated parameters, the attacker instructs the cstecgi.cgi handler to invoke the showSyslog function.\nBecause the function lacks the necessary authorization logic, the underlying system service executes the command to retrieve the internal system log buffer. The device then encapsulates the contents of these logs within the HTTP response, transmitting them back to the unauthenticated source.\nFrom an exploitation perspective, this is a low-complexity attack requiring no specialized authentication headers or administrative privileges. The network exposure is broad, as the cstecgi.cgi endpoint is typically accessible over HTTP/HTTPS from the local network interface or, in cases of poor perimeter configuration, directly from the Wide Area Network (WAN) interface.\nThe payload behavior is strictly defined by the target's internal logging mechanism. By triggering this function, an attacker can dump the most recent entries of the system logs. These logs often include persistent state information, DHCP assignments, connection attempts, and potentially diagnostic errors that leak environmental information useful for pivoting or staging further attacks against the device or the local network segment.\nPost-exploitation, the attacker gains visibility into the device's operational history. This data can be correlated with other network observation techniques to profile the user's internet activity or identify specific vulnerabilities in internal services currently active on the device."
}