Description

Incorrect access control in the informSlaveUpdate function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to trigger mesh slave update coordination via sending a crafted POST request to /cgi-bin/cstecgi.cgi.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.8",
  "pubDate": "2026-08-31T20:17:04.670Z",
  "pubdate": "2026-08-31T20:17:04.670Z",
  "executiveSummary": "The TOTOLINK T6 router, specifically firmware version 4.1.5cu.748_B20211015, contains a critical vulnerability stemming from improper access control within the informSlaveUpdate function.\nThis security flaw enables unauthenticated remote attackers to initiate unauthorized mesh slave update coordination processes.\nBy sending a specifically crafted POST request to the /cgi-bin/cstecgi.cgi endpoint, an attacker can manipulate system operations without requiring valid authentication credentials.\nThe primary risk implications involve the potential for unauthorized network configuration changes and potential disruption of mesh networking services.\nThis vulnerability is particularly dangerous as it is accessible over the network without prior authentication, effectively lowering the barrier for exploitation by malicious actors.\nSuccessful exploitation allows attackers to bypass security boundaries, potentially leading to denial-of-service conditions or the orchestration of illegitimate firmware synchronization activities within the local network segment.",
  "technicalDetails": "The vulnerability resides within the binary logic of the /cgi-bin/cstecgi.cgi script, which serves as the primary gateway for administrative functions in the TOTOLINK T6 ecosystem.\nThe root cause is the lack of session validation or cryptographic verification in the informSlaveUpdate function, which is exposed to external requests via the common gateway interface (CGI).\nNormally, sensitive system functions within the T6 firmware are gated by session tokens or cookie-based authentication checks; however, the informSlaveUpdate handler fails to verify the session state of the request initiator, granting unauthorized access to the underlying function logic.\nAn attacker can exploit this by crafting a malicious HTTP POST request targeted at /cgi-bin/cstecgi.cgi. The request must include parameters that the back-end logic interprets as a valid command for the mesh synchronization module.\nThe attack flow proceeds as follows: First, the attacker identifies the network address of the vulnerable device. Second, the attacker crafts a POST request with specific key-value pairs formatted to reach the informSlaveUpdate function path. Third, the request is dispatched to the /cgi-bin/cstecgi.cgi handler without an authentication header or valid session cookie. Finally, the application, failing to perform an access control check, proceeds to execute the mesh update sequence.\nThe vulnerable component is the cstecgi binary responsible for routing requests to internal function pointers. Because this function is invoked prematurely in the execution chain—before authentication modules have validated the request—the device performs the requested coordination tasks blindly.\nThe impact of this vulnerability is significant in a mesh networking environment. By triggering unauthenticated slave updates, an attacker could potentially force devices to connect to rogue or misconfigured nodes, perform firmware downgrade attacks if update verification is insufficient, or cause localized network instability.\nThe exposure is widespread for any device accessible over the local area network (LAN) or via Wide Area Network (WAN) interfaces if the administrative portal is exposed. Given the lack of required privileges, any entity capable of sending HTTP traffic to the device can trigger this flaw.\nPost-exploitation, the attacker gains control over the mesh coordination state, which can be utilized to disrupt network topology or facilitate further reconnaissance within the managed network segments."
}