CVE-2026-76857 Overview
CVE-2026-76857 is a sensitive information disclosure vulnerability in Netcore NR255-V router firmware version 1.5.130703. The flaw resides in the ddns_wan_list_show.cgi endpoint and associated DDNSset_cgi, IGD_GetCgiHandler, and IGD_CgiCall components. An authenticated attacker who reaches this Common Gateway Interface (CGI) handler can retrieve plaintext Dynamic DNS (DDNS) credentials stored on the device. The exposed account information can enable takeover of the DDNS provider account and pivoting to services that rely on that DNS namespace. This weakness is categorized under [CWE-522: Insufficiently Protected Credentials].
Critical Impact
Attackers reaching the vulnerable CGI handler recover plaintext DDNS credentials, enabling account compromise and downstream DNS-based abuse.
Affected Products
- Netcore NR255-V router
- Firmware version 1.5.130703
- ddns_wan_list_show.cgi handler and related DDNSset_cgi, IGD_GetCgiHandler, and IGD_CgiCall components
Discovery Timeline
- 2026-09-15 - CVE-2026-76857 published to the National Vulnerability Database (NVD)
- 2026-09-17 - Last updated in NVD database
Technical Details for CVE-2026-76857
Vulnerability Analysis
The Netcore NR255-V web management interface exposes a CGI endpoint, ddns_wan_list_show.cgi, that returns the current DDNS Wide Area Network (WAN) configuration list. The handler serializes stored DDNS account records without redacting secret fields. Credentials configured for the DDNS provider are returned in cleartext within the response body.
The request path flows through IGD_CgiCall and IGD_GetCgiHandler, which route to DDNSset_cgi handlers responsible for reading persisted DDNS state. Because the persisted state itself is stored unencrypted and the handler performs no output filtering, the username and password associated with the DDNS account are echoed to any caller reaching the endpoint.
An attacker with low-privilege access to the management interface, or who can reach it across a network segment where the router is exposed, can request the endpoint and harvest credentials. The exposed accounts can be reused to hijack the associated DNS namespace, redirect traffic, or acquire valid TLS certificates for domains under attacker control.
Root Cause
The root cause is insufficient protection of stored authentication material combined with unfiltered CGI output. Sensitive DDNS credentials are persisted in the device configuration in cleartext and rendered verbatim by ddns_wan_list_show.cgi. No masking, hashing, or access segmentation exists between administrative UI rendering and the raw credential store.
Attack Vector
Exploitation requires network reachability to the router's HTTP management interface and low-privilege authenticated access. The attacker issues a request to ddns_wan_list_show.cgi and parses the response to extract the plaintext DDNS username and password. No memory corruption, injection, or user interaction is required.
Refer to the VulnCheck advisory on the DDNS credential disclosure and the public GitHub reference for endpoint details.
Detection Methods for CVE-2026-76857
Indicators of Compromise
- HTTP GET requests to /ddns_wan_list_show.cgi originating from unexpected internal hosts or external addresses.
- HTTP responses from the router that contain DDNS provider hostnames alongside credential-shaped fields.
- Unexpected DDNS record changes at the provider that do not correspond to router reboots or configuration edits.
Detection Strategies
- Inspect web-server access logs on the router or upstream proxies for requests to ddns_wan_list_show.cgi and correlate against authorized administrator sessions.
- Alert on any external source address contacting the router management interface, particularly requests targeting DDNSset_cgi or related IGD handlers.
- Monitor DDNS provider audit logs for logins from IP addresses that do not match the router's outbound WAN address.
Monitoring Recommendations
- Forward router HTTP access logs and authentication events to a centralized log store for retention and correlation.
- Baseline normal administrative access patterns and flag deviations in source geography, user agent, or request frequency.
- Track DNS resolution changes for hostnames managed through the DDNS account to identify unauthorized record modifications.
How to Mitigate CVE-2026-76857
Immediate Actions Required
- Restrict access to the router management interface to trusted management VLANs and block WAN-side exposure.
- Rotate the DDNS provider account credentials configured on affected NR255-V devices and enable multi-factor authentication at the provider where supported.
- Audit DDNS provider records and recent logins for signs of unauthorized use.
Patch Information
No vendor patch is referenced in the available advisories for firmware version 1.5.130703. Consult the VulnCheck advisory for status updates and monitor the Netcore vendor site for firmware releases addressing the ddns_wan_list_show.cgi handler.
Workarounds
- Disable the DDNS feature on the router if it is not required, removing the stored credentials from device configuration.
- Place the router management interface behind a network access control list that permits only specific administrative source addresses.
- Use a dedicated, low-privilege DDNS provider account scoped to a single hostname to limit the blast radius if credentials are recovered.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
