CVE-2026-4543 Overview
CVE-2026-4543 is a command injection vulnerability in the Wavlink WL-WN578W2 wireless router running firmware version 221110. The flaw resides in the /cgi-bin/firewall.cgi endpoint, where the POST request handler fails to sanitize the dmz_flag and del_flag parameters. An authenticated remote attacker can manipulate these arguments to inject operating system commands that execute in the device context. Public exploit details have been released, and the vendor did not respond to disclosure attempts. The vulnerability is classified under [CWE-74] (Improper Neutralization of Special Elements in Output).
Critical Impact
Remote attackers with low privileges can inject arbitrary OS commands through firewall.cgi, compromising confidentiality, integrity, and availability of affected Wavlink WL-WN578W2 devices.
Affected Products
- Wavlink WL-WN578W2 hardware
- Wavlink WL-WN578W2 firmware version 221110
- Deployments exposing the device web management interface
Discovery Timeline
- 2026-03-22 - CVE-2026-4543 published to NVD
- 2026-04-30 - Last updated in NVD database
Technical Details for CVE-2026-4543
Vulnerability Analysis
The vulnerability exists in the POST request handler of /cgi-bin/firewall.cgi, a CGI binary on the Wavlink WL-WN578W2 router. The handler processes the dmz_flag and del_flag parameters without input validation or output neutralization. An attacker submits a crafted POST request containing shell metacharacters in either parameter. The CGI passes the tainted input into an underlying system call, resulting in command execution under the privileges of the web server process, typically root on embedded routers.
The exploit has been documented in public proof-of-concept repositories. The Exploit Prediction Scoring System (EPSS) places this vulnerability in the 71st percentile, indicating measurable real-world exploitation likelihood despite the low base score.
Root Cause
The root cause is improper neutralization of special elements passed to a downstream component [CWE-74]. The firmware concatenates user-supplied dmz_flag and del_flag values directly into shell command strings invoked by system() or an equivalent function. No allowlist, escaping, or parameterization separates user input from command syntax.
Attack Vector
The attack is remote and network-based. An attacker with low-level credentials on the router web interface sends a malicious POST request to /cgi-bin/firewall.cgi. By embedding shell separators such as ;, |, or backticks in the dmz_flag or del_flag argument, the attacker chains arbitrary commands onto the legitimate firewall configuration logic. Successful exploitation yields command execution on the device, enabling persistence, traffic interception, or pivoting into the connected network.
No verified exploit code is reproduced here. Technical details are available in the VulDB entry #352360 and the GitHub PoC repository for vul_4 and vul_5.
Detection Methods for CVE-2026-4543
Indicators of Compromise
- POST requests to /cgi-bin/firewall.cgi containing shell metacharacters (;, |, &, backticks, $()) within the dmz_flag or del_flag parameter values.
- Unexpected outbound connections from the router to attacker-controlled infrastructure following firewall configuration changes.
- Modified or newly created files in router-writable directories such as /tmp or /var after web interface access.
Detection Strategies
- Inspect HTTP request logs on upstream proxies or network sensors for POST payloads to firewall.cgi containing non-alphanumeric characters in the dmz_flag and del_flag fields.
- Deploy network signatures that flag CGI requests carrying URL-encoded shell separators targeting Wavlink management endpoints.
- Correlate router authentication events with subsequent administrative POST requests to identify low-privilege accounts performing firewall manipulation.
Monitoring Recommendations
- Capture and retain full HTTP request bodies for traffic destined to router management interfaces on segmented administrative VLANs.
- Alert on any router-originated DNS or HTTP connections to non-allowlisted destinations.
- Monitor for firmware integrity drift by periodically validating router configuration exports against known-good baselines.
How to Mitigate CVE-2026-4543
Immediate Actions Required
- Remove the Wavlink WL-WN578W2 web management interface from any untrusted network and restrict access to a dedicated administrative subnet.
- Change all default and low-privilege account credentials on the device, since exploitation requires authenticated access.
- Audit existing devices running firmware 221110 for signs of unauthorized configuration changes or unknown processes.
Patch Information
No vendor patch is available. The CVE record states the vendor was contacted early in the disclosure process but did not respond. Organizations should treat the affected firmware as end-of-support for security purposes and plan device replacement with a supported platform.
Workarounds
- Disable remote administration and bind the web interface strictly to a trusted LAN segment.
- Place the router behind a reverse proxy or web application firewall that strips shell metacharacters from POST parameters targeting /cgi-bin/firewall.cgi.
- Replace affected WL-WN578W2 units with hardware from a vendor providing active security maintenance where feasible.
# Example firewall rule to restrict router admin interface access
# Replace 192.0.2.10 with the authorized management workstation IP
iptables -A INPUT -p tcp --dport 80 -s 192.0.2.10 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.0.2.10 -j ACCEPT
iptables -A INPUT -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.
