Description

A vulnerability has been found in TOTOLINK N600R 4.3.0cu.7866_B20220506. This vulnerability affects the function loginAuth of the file /web_cste/cgi-bin/cstecgi.cgi of the component Authentication Handler. Such manipulation leads to insufficiently random values. It is possible to launch the attack remotely. This attack is characterized by high complexity. It is stated that the exploitability is difficult. The exploit has been disclosed to the public and may be used.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "3.7",
  "pubDate": "2026-08-30T18:17:00.380Z",
  "pubdate": "2026-08-30T18:17:00.380Z",
  "executiveSummary": "The TOTOLINK N600R, specifically firmware version 4.3.0cu.7866_B20220506, contains a critical security vulnerability within its authentication mechanism.\nThe vulnerability stems from the use of insufficiently random values during the authentication process managed by the loginAuth function.\nThis flaw resides in the /web_cste/cgi-bin/cstecgi.cgi component, which serves as a critical authentication handler for the device.\nBy manipulating the session token or authentication parameters due to poor entropy, a remote, unauthenticated attacker could potentially bypass authentication controls or hijack user sessions.\nAlthough the vulnerability is characterized by high complexity and difficult exploitability, its public disclosure increases the risk of exploitation by sophisticated threat actors.\nThe impact includes unauthorized administrative access, full device compromise, and the potential for remote code execution or unauthorized configuration changes, effectively undermining the security posture of the affected networking hardware.",
  "technicalDetails": "The vulnerability is located in the loginAuth function within the /web_cste/cgi-bin/cstecgi.cgi CGI script on the TOTOLINK N600R running firmware version 4.3.0cu.7866_B20220506. The root cause is the implementation of a weak pseudorandom number generator (PRNG) or the misuse of seeding mechanisms when generating session identifiers or authentication tokens.\nIn typical web-based embedded management interfaces, authentication security relies on the generation of high-entropy, unpredictable tokens to ensure session integrity. When the entropy source is insufficient, the resulting tokens become deterministic or fall within a predictable space. An attacker can perform offline analysis of captured authentication exchange sequences to identify patterns or compute future valid tokens.\nThe attack flow begins with the adversary interacting with the remote administrative interface over HTTP/HTTPS. By monitoring the loginAuth function's output, the attacker observes the token generation process. Because the underlying entropy source for these values lacks sufficient randomness, the generated session tokens exhibit statistical bias. The attacker leverages this to predict current or future session identifiers.\nExploitation involves the following sequence: First, the attacker initiates multiple authentication attempts to gather a sufficiently large sample size of generated tokens. Second, the attacker performs cryptanalysis or statistical modeling on the collected sample to derive the underlying state of the PRNG. Third, once the state is reconstructed, the attacker generates a valid token corresponding to an authorized administrative session. Finally, the attacker injects this forged token into the HTTP header of subsequent requests to the cstecgi.cgi handler. If successful, the server-side logic validates the forged token as legitimate, granting the attacker unauthorized access to the device's management interface.\nThe exploitability is rated as difficult due to the requirement for specific timing or a significant volume of intercepted traffic to overcome the high-complexity barriers associated with the token generation logic. However, since the exploit is publicly disclosed, the barrier to entry for attackers is significantly lowered. The post-exploitation impact allows for the modification of router configurations, redirection of traffic, and the potential installation of persistence mechanisms, enabling full control over the network traffic passing through the device."
}