CVE-2026-15511: Comfast CF-WR631AX RCE Vulnerability

CVE-2026-15511 Overview

CVE-2026-15511 is an OS command injection vulnerability [CWE-77] in the Comfast CF-WR631AX V3 router through firmware version 2.7.0.8. The flaw resides in the system_wl_upload_pic_file function within /usr/bin/webmgnt, part of the FastCGI backend that handles the WiFi portal image upload feature. Attackers manipulate the filename argument to inject arbitrary operating system commands. The vulnerability is exploitable remotely without authentication or user interaction. A public proof-of-concept has been disclosed on GitHub, and the vendor did not respond to disclosure attempts.

Critical Impact
Unauthenticated remote attackers can execute arbitrary OS commands on affected Comfast CF-WR631AX V3 routers, resulting in full device compromise.

Affected Products

Comfast CF-WR631AX V3 router
Firmware versions up to and including 2.7.0.8
FastCGI backend component /usr/bin/webmgnt

Discovery Timeline

2026-07-12 - CVE-2026-15511 published to NVD
2026-07-14 - Last updated in NVD database

Technical Details for CVE-2026-15511

Vulnerability Analysis

The vulnerability is an OS command injection flaw in the WiFi portal image upload handler. The system_wl_upload_pic_file function inside the /usr/bin/webmgnt FastCGI binary processes uploaded image files without properly sanitizing the filename parameter. Attacker-supplied shell metacharacters embedded in the filename are passed to an underlying shell interpreter, resulting in arbitrary command execution under the privileges of the web management process, typically root on embedded router firmware.

Command injection on router firmware provides an immediate path to full device takeover. Attackers can pivot into the internal network, harvest credentials, modify routing and DNS settings, or enlist the device into a botnet. The public disclosure of the proof-of-concept increases the likelihood of opportunistic scanning and exploitation.

Root Cause

The root cause is missing input validation and sanitization on the filename argument passed to the system_wl_upload_pic_file function. The function constructs an OS command string that incorporates the untrusted filename value and passes it to a shell without escaping metacharacters such as `, $(), ;, |, or &.

Attack Vector

An unauthenticated remote attacker sends a crafted HTTP request to the WiFi portal image upload endpoint served by the FastCGI backend. By embedding shell metacharacters in the filename parameter, the attacker forces the router to execute arbitrary commands. Because the router web interface is often reachable on the LAN, and in some deployments on the WAN, exposure is high. The vulnerability mechanism is described in the public proof-of-concept at the GitHub PoC Repository and the VulDB CVE-2026-15511 entry.

Detection Methods for CVE-2026-15511

Indicators of Compromise

HTTP POST requests to the WiFi portal image upload endpoint containing shell metacharacters (;, |, `, $(), &&) in the filename parameter.
Unexpected child processes spawned by /usr/bin/webmgnt, such as sh, wget, curl, nc, or tftp.
New listening sockets, reverse shell connections, or outbound traffic to attacker-controlled infrastructure originating from the router.
Modifications to router configuration files, DNS settings, or firmware images without administrator action.

Detection Strategies

Inspect web server and FastCGI access logs for image upload requests carrying suspicious filename values or non-image extensions.
Deploy network intrusion detection signatures that match command injection patterns in multipart form-data filename fields.
Correlate router egress traffic with threat intelligence feeds to surface communication with known command-and-control hosts.

Monitoring Recommendations

Enable syslog forwarding from the router to a centralized log platform and alert on process execution anomalies.
Monitor for unauthenticated access attempts to /usr/bin/webmgnt upload endpoints, especially from external IP ranges.
Baseline normal outbound connections from network appliances and alert on deviations that suggest post-exploitation activity.

How to Mitigate CVE-2026-15511

Immediate Actions Required

Restrict access to the router management interface to trusted management VLANs and block WAN-side administrative access.
Disable the WiFi portal image upload functionality if it is not required for operations.
Rotate administrative credentials and audit router configuration for unauthorized modifications.
Isolate exposed CF-WR631AX V3 devices from sensitive network segments until a fix is available.

Patch Information

No vendor patch is currently available. According to the VulDB Vulnerability Report, the vendor was contacted early about this disclosure but did not respond. Organizations should monitor the Comfast website for firmware updates and consider replacing affected devices if a patch is not released.

Workarounds

Place the router behind a network firewall that filters unsolicited inbound HTTP and FastCGI traffic.
Apply access control lists to permit management interface access only from specific administrator workstations.
Deploy a web application firewall in front of the management interface to block requests containing shell metacharacters in upload parameters.
Segment IoT and consumer-grade networking equipment away from production and identity infrastructure to limit blast radius if the device is compromised.

bash

# Example iptables rule to restrict router management access to a trusted subnet
iptables -A INPUT -p tcp --dport 80 -s 192.0.2.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.0.2.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP