CVE-2026-7750 Overview
CVE-2026-7750 is a buffer overflow vulnerability in the Totolink N300RH router running firmware version 3.2.4-B20220812. The flaw resides in the setMacFilterRules function within /cgi-bin/cstecgi.cgi, part of the device's POST request handler. Attackers can manipulate the mac_address argument to trigger memory corruption [CWE-119]. The vulnerability is remotely exploitable over the network and requires only low-level privileges. Public exploit details have been disclosed, increasing the risk of opportunistic exploitation against exposed devices.
Critical Impact
Remote attackers with low privileges can corrupt memory in the router's web management interface, potentially leading to arbitrary code execution or device compromise on affected Totolink N300RH devices.
Affected Products
- Totolink N300RH router
- Firmware version 3.2.4-B20220812
- /cgi-bin/cstecgi.cgi POST request handler component
Discovery Timeline
- 2026-05-04 - CVE-2026-7750 published to NVD
- 2026-05-04 - Last updated in NVD database
Technical Details for CVE-2026-7750
Vulnerability Analysis
The vulnerability exists in the setMacFilterRules handler exposed through the CGI binary /cgi-bin/cstecgi.cgi on the Totolink N300RH router. The handler processes POST requests containing a mac_address parameter used to populate MAC filter rules. The input is copied into a fixed-size buffer without proper length validation, producing a classic buffer overflow condition classified under [CWE-119]. An authenticated attacker submitting an oversized mac_address value can overwrite adjacent memory in the CGI process. Because embedded router firmware typically runs without modern memory protections such as ASLR or non-executable stacks, this overflow can lead to control-flow hijacking. The exploit details are public, lowering the barrier for attackers.
Root Cause
The root cause is missing bounds checking on the mac_address argument before it is copied into a stack or heap buffer inside the setMacFilterRules function. The CGI handler trusts client-supplied length and content, which violates safe input validation practices for embedded web interfaces.
Attack Vector
Exploitation requires network access to the router's web management interface and low-privilege authentication. The attacker sends a crafted POST request to /cgi-bin/cstecgi.cgi invoking setMacFilterRules with an oversized mac_address payload. Successful manipulation corrupts memory and can affect confidentiality, integrity, and availability of the device. The vulnerability mechanism is documented in the Notion technical writeup and the VulDB vulnerability entry. No verified proof-of-concept code is reproduced here.
Detection Methods for CVE-2026-7750
Indicators of Compromise
- POST requests to /cgi-bin/cstecgi.cgi containing unusually long mac_address field values exceeding standard 17-character MAC notation.
- HTTP requests invoking setMacFilterRules from external or unexpected source addresses.
- Unexpected reboots, web interface crashes, or httpd/CGI process restarts on the Totolink N300RH router.
- New or modified MAC filter rules that were not authorized by an administrator.
Detection Strategies
- Inspect router HTTP and syslog output for repeated POST traffic to cstecgi.cgi with anomalous payload sizes.
- Deploy network IDS signatures that flag malformed or oversized mac_address parameters in CGI POST bodies.
- Correlate router crash events with administrative interface activity to identify probing attempts.
Monitoring Recommendations
- Forward router and firewall logs to a centralized SIEM and alert on management interface access from non-administrative networks.
- Monitor outbound traffic from the router for signs of post-exploitation activity such as connections to unfamiliar command-and-control hosts.
- Track firmware versions across managed devices and alert when vulnerable builds remain in production.
How to Mitigate CVE-2026-7750
Immediate Actions Required
- Restrict access to the router's web management interface to trusted internal networks and disable WAN-side administration.
- Change default and weak administrator credentials to reduce the risk of low-privilege attackers reaching the vulnerable handler.
- Audit existing MAC filter rules and recent configuration changes for tampering.
- Segment the router from sensitive internal assets pending a vendor patch.
Patch Information
No vendor patch is referenced in the published CVE data. Administrators should monitor the TOTOLINK official site for firmware updates addressing the setMacFilterRules buffer overflow and apply them as soon as they are released.
Workarounds
- Disable remote management of the device over the WAN interface.
- Place the router behind an upstream firewall that blocks unsolicited inbound HTTP/HTTPS to the management port.
- Replace end-of-support or unpatched Totolink N300RH devices with supported hardware where a vendor fix is unavailable.
# Configuration example: block external access to the router management interface
iptables -A INPUT -i wan0 -p tcp --dport 80 -j DROP
iptables -A INPUT -i wan0 -p tcp --dport 443 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
