CVE-2026-51660 Overview
CVE-2026-51660 is an incorrect access control vulnerability in the getIpPortFilterRules function of the TOTOLINK T6 router firmware version 4.1.5cu.748_B20211015. The flaw allows unauthenticated remote attackers to retrieve IP and port filtering rules by sending a crafted POST request to /cgi-bin/cstecgi.cgi. The vulnerability is categorized under [CWE-284] (Improper Access Control) and is exploitable over the network without user interaction or privileges.
Critical Impact
Unauthenticated attackers can retrieve sensitive network filtering configuration remotely, exposing internal network topology and firewall policy to reconnaissance.
Affected Products
- TOTOLINK T6 router
- Firmware version 4.1.5cu.748_B20211015
- CGI endpoint /cgi-bin/cstecgi.cgi
Discovery Timeline
- 2026-08-28 - CVE-2026-51660 published to NVD
- 2026-09-01 - Last updated in NVD database
Technical Details for CVE-2026-51660
Vulnerability Analysis
The TOTOLINK T6 router exposes an HTTP CGI interface at /cgi-bin/cstecgi.cgi that dispatches requests to internal handler functions based on parameters in the POST body. The getIpPortFilterRules handler returns the router's active IP and port filtering rules. The handler does not verify that the caller has an authenticated administrative session before returning this data.
An attacker with network reachability to the router's management interface can send a single crafted POST request and receive the configured filter rules in the response. Disclosure of these rules reveals internal IP ranges, permitted or blocked services, and network segmentation policies. This information supports subsequent targeted attacks against hosts behind the router.
Root Cause
The root cause is a missing authorization check inside the getIpPortFilterRules request handler within cstecgi.cgi. Sensitive configuration endpoints on the TOTOLINK T6 should require a valid authenticated session token, but this handler processes requests before enforcing that check. The design flaw maps to [CWE-284] Improper Access Control.
Attack Vector
Exploitation requires only network access to the router's HTTP interface. An attacker sends a POST request to /cgi-bin/cstecgi.cgi with a body specifying the getIpPortFilterRules action. The device processes the request and returns the filtering rules in the HTTP response body. No credentials, tokens, or session cookies are required. Technical details are referenced in the TOTOLINK Vendor Coordination Repository and a mirror coordination repository.
No verified public proof-of-concept code is available at this time. See the vendor coordination references above for additional technical detail.
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Stop Identity AttacksDetection Methods for CVE-2026-51660
Indicators of Compromise
- Unauthenticated POST requests to /cgi-bin/cstecgi.cgi containing the string getIpPortFilterRules in the request body.
- HTTP requests to the router management interface originating from external or untrusted network segments.
- Sequential CGI probe requests targeting multiple handler names against cstecgi.cgi.
Detection Strategies
- Inspect web server or reverse-proxy logs on the router upstream for POST requests to /cgi-bin/cstecgi.cgi that lack a valid authentication cookie or session token.
- Deploy network intrusion detection signatures that match the getIpPortFilterRules action name in HTTP POST bodies destined for TOTOLINK devices.
- Alert on any external source addresses reaching the router's HTTP management port, which should not be exposed to the internet.
Monitoring Recommendations
- Forward router and perimeter firewall logs to a centralized log platform for correlation and retention.
- Monitor for outbound traffic patterns consistent with post-reconnaissance activity, such as scans against internal IPs disclosed by leaked filter rules.
- Track firmware version inventory for TOTOLINK T6 devices and flag any running 4.1.5cu.748_B20211015 or earlier.
How to Mitigate CVE-2026-51660
Immediate Actions Required
- Restrict access to the router's HTTP management interface to trusted management VLANs or specific administrative hosts only.
- Disable remote (WAN-side) management on affected TOTOLINK T6 devices until a patched firmware is applied.
- Rotate any credentials, pre-shared keys, or network configuration values that may be inferred from disclosed filtering rules.
Patch Information
No vendor-confirmed patched firmware is referenced in the NVD entry at the time of publication. Check the TOTOLINK official website and the TOTOLINK download page for updated firmware for the T6 model. Apply any newer firmware that supersedes 4.1.5cu.748_B20211015 once the vendor addresses the missing authorization check in cstecgi.cgi.
Workarounds
- Place the router management interface behind a firewall rule that blocks all inbound access except from designated administrative subnets.
- Use an upstream device to filter POST requests to /cgi-bin/cstecgi.cgi that contain the getIpPortFilterRules action from untrusted sources.
- Replace affected TOTOLINK T6 units with supported hardware if no firmware update is released.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
