Attack Chain

1. An unauthenticated remote attacker sends a specially crafted HTTP POST request to the web management interface of the Comfast CF-WR631AX V3 router.
2. The request targets the system_wl_upload_pic_file function, which is handled by the /usr/bin/webmgnt FastCGI Backend component.
3. The attacker includes OS command injection payloads within the filename argument of the HTTP request, bypassing input validation.
4. The vulnerable function processes the malicious filename argument, leading to the execution of arbitrary operating system commands on the router with elevated privileges.
5. The attacker gains full control over the Comfast CF-WR631AX V3 router, achieving remote code execution.
6. The compromised router can then be used as a pivot point for further attacks within the internal network, perform data exfiltration, or alter network traffic.

Impact

Successful exploitation of CVE-2026-15511 grants an unauthenticated remote attacker full control over the affected Comfast CF-WR631AX V3 router. This can lead to complete device compromise, allowing threat actors to intercept network traffic, reroute connections, inject malicious content, or establish persistent access to the local network. Organizations and individuals using these devices are at high risk of network-wide breaches, data theft, and further malicious activity originating from the compromised router.

Recommendation

• Immediately disconnect Comfast CF-WR631AX V3 routers from internet-facing networks if patching is not available.
• Monitor web server logs for the /webmgnt endpoint for suspicious POST requests containing OS command injection patterns as described in the "Detects CVE-2026-15511 Exploitation" Sigma rule.
• Deploy the Sigma rule "Detects CVE-2026-15511 Exploitation - Comfast Router OS Command Injection" to your SIEM and tune for your environment to detect exploitation attempts.