CVE-2026-7717 Overview
CVE-2026-7717 is a buffer overflow vulnerability affecting the TOTOLINK WA300 wireless access point running firmware version 5.2cu.7112_B20190227. The flaw resides in the UploadCustomModule function within /cgi-bin/cstecgi.cgi, which is reachable through the device's POST request handler. An attacker can manipulate the File argument to overflow a fixed-size buffer and corrupt adjacent memory. The issue is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). The exploit has been publicly disclosed, increasing the likelihood of opportunistic targeting against exposed devices.
Critical Impact
Remote attackers with low privileges can trigger memory corruption in UploadCustomModule, potentially leading to arbitrary code execution on the affected router and full compromise of the device.
Affected Products
- TOTOLINK WA300 wireless access point
- Firmware version 5.2cu.7112_B20190227
- Component: POST request handler in /cgi-bin/cstecgi.cgi
Discovery Timeline
- 2026-05-04 - CVE-2026-7717 published to NVD
- 2026-05-04 - Last updated in NVD database
Technical Details for CVE-2026-7717
Vulnerability Analysis
The vulnerability lies in the UploadCustomModule handler exposed by the CGI binary cstecgi.cgi. The function processes user-supplied data from POST requests without enforcing proper bounds on the File parameter. When an attacker submits a request containing an oversized File argument, the routine writes the value into a fixed-size stack or heap buffer. The write operation exceeds the allocated buffer length and corrupts adjacent memory regions. This memory corruption can disrupt control flow on the embedded MIPS-based device.
Root Cause
The root cause is the absence of length validation on the File parameter before it is copied into a buffer. The handler likely uses unsafe string-handling routines such as strcpy or sprintf without checking input size. CWE-119 captures this category of memory corruption where operations are performed outside the bounds of allocated memory. Embedded device firmware frequently exhibits this pattern because vendor CGI binaries process untrusted HTTP input directly.
Attack Vector
The attack is delivered over the network through the device's HTTP management interface. An attacker sends a crafted POST request to /cgi-bin/cstecgi.cgi invoking UploadCustomModule with an oversized File argument. The CVSS v4.0 vector indicates that low privileges are required, meaning an authenticated session or weak default credentials are sufficient. Successful exploitation can yield denial of service and, with reliable offset alignment, arbitrary code execution within the router's web service context. Refer to the Notion Custom Module Guide and VulDB Vulnerability #360893 for the disclosed proof of concept.
No verified exploit code is reproduced here. The publicly disclosed proof of concept manipulates the File POST parameter to exceed the expected length and trigger memory corruption inside UploadCustomModule.
Detection Methods for CVE-2026-7717
Indicators of Compromise
- POST requests to /cgi-bin/cstecgi.cgi containing an unusually long File parameter value.
- Unexpected restarts or crashes of the cstecgi.cgi process or the device's HTTP daemon.
- Outbound connections from the router to unfamiliar IP addresses following management-interface traffic.
- Configuration changes or new firmware modules appearing without administrator action.
Detection Strategies
- Inspect HTTP request bodies destined for /cgi-bin/cstecgi.cgi and flag File arguments exceeding reasonable size thresholds.
- Deploy network IDS rules that match the UploadCustomModule action combined with oversized POST payloads.
- Correlate router crash telemetry with preceding inbound HTTP traffic from external sources.
Monitoring Recommendations
- Restrict and log access to the WA300 administrative interface from any untrusted network segment.
- Forward router syslog data to a centralized SIEM for anomaly analysis on management-plane events.
- Track repeated authentication attempts against the device, since the attacker requires a valid low-privilege session.
How to Mitigate CVE-2026-7717
Immediate Actions Required
- Remove the WA300 administrative interface from the public internet and limit access to a trusted management VLAN.
- Replace default and weak credentials on the device to raise the bar for the low-privilege precondition.
- Audit existing sessions and configuration on affected devices for signs of tampering.
- Consider replacing the WA300 if vendor patches remain unavailable for the affected firmware build.
Patch Information
At the time of publication, no fixed firmware version has been linked in the NVD entry for 5.2cu.7112_B20190227. Monitor the TOTOLINK Official Website for updated firmware addressing the UploadCustomModule buffer overflow. Additional tracking is available through the VulDB Vulnerability #360893 entry.
Workarounds
- Block external access to TCP ports serving the WA300 web interface using upstream firewall rules.
- Disable remote management features on the device until a vendor fix is published.
- Place the device behind a reverse proxy or VPN that enforces strict authentication before reaching /cgi-bin/cstecgi.cgi.
- Apply network segmentation so the router cannot initiate arbitrary outbound traffic to internal assets.
# Example upstream firewall rule to restrict WA300 management access
# Replace 192.0.2.0/24 with your trusted management subnet
iptables -A FORWARD -p tcp -d <WA300_IP> --dport 80 -s 192.0.2.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d <WA300_IP> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <WA300_IP> --dport 443 -s 192.0.2.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d <WA300_IP> --dport 443 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
