Wavlink WL-WN579X3-C Stack-Based Buffer Overflow Vulnerability

A critical vulnerability, identified as CVE-2026-5004, affects the Wavlink WL-WN579X3-C 231124 router. The vulnerability lies within the UPNP Handler component, specifically the /cgi-bin/firewall.cgi file’s sub_4019FC function. By manipulating the UpnpEnabled argument, a remote attacker can trigger a stack-based buffer overflow. This can lead to arbitrary code execution on the device. Public exploits for this vulnerability are available, increasing the risk of widespread exploitation. Despite responsible disclosure attempts, the vendor has not provided a patch or response, leaving users vulnerable. This is a significant concern for network security, especially for devices exposed to the internet.

Attack Chain

1. The attacker identifies a vulnerable Wavlink WL-WN579X3-C 231124 router exposed to the internet.
2. The attacker crafts a malicious HTTP request targeting /cgi-bin/firewall.cgi.
3. The HTTP request includes a manipulated UpnpEnabled argument designed to overflow the buffer in the sub_4019FC function.
4. The vulnerable sub_4019FC function processes the UpnpEnabled argument without proper bounds checking.
5. The buffer overflow occurs, overwriting adjacent memory on the stack, including the return address.
6. The overwritten return address points to attacker-controlled code.
7. Upon function return, execution jumps to the attacker-controlled code, allowing arbitrary commands to be executed.
8. The attacker gains remote code execution, potentially allowing complete control of the device, including network access and data exfiltration.

Impact

Successful exploitation of CVE-2026-5004 allows a remote attacker to execute arbitrary code on the vulnerable Wavlink WL-WN579X3-C 231124 router. This could lead to complete device compromise, including unauthorized network access, data exfiltration, and the potential use of the router as a botnet node. Given the availability of public exploits, a widespread exploitation is possible, affecting potentially thousands of devices. The lack of vendor response exacerbates the risk, as no official patch is available.

Recommendation

• Deploy the Sigma rule Detect Suspicious Firewall CGI Requests to your SIEM and tune for your environment to identify potential exploitation attempts targeting the /cgi-bin/firewall.cgi endpoint.
• Deploy the Sigma rule Detect UPNP Enabled Overflow to detect possible overflows.
• Monitor web server logs for requests to /cgi-bin/firewall.cgi with unusually long UpnpEnabled parameters.
• If possible, isolate Wavlink WL-WN579X3-C 231124 routers from direct internet exposure until a patch is available.