CVE-2026-74843 in WN531P3
Summary
by MITRE • 08/17/2026
A vulnerability was determined in Wavlink WN531P3 and WN535M1 V250922. Affected by this vulnerability is the function strcpy of the file /etc/lighttpd/www/cgi-bin/export_pingortrace.cgi of the component Export Pingortrace CGI. Executing a manipulation of the argument HTTP_COOKIE can lead to stack-based buffer overflow. The attack may be launched remotely. The exploit has been publicly disclosed and may be utilized. The vendor was contacted early about this disclosure.
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Analysis
by VulDB Data Team • 08/24/2026
The vulnerability identified in Wavlink WN531P3 and WN535M1 devices running firmware version V250922 represents a critical security flaw within the device's web management interface, specifically affecting the Export Pingortrace CGI component. This issue stems from improper input validation and boundary checking implemented by the developers of the embedded Linux-based router software. The core technical defect resides in the use of the strcpy function located within the file /etc/lighttpd/www/cgi-bin/export_pingortrace.cgi. In C programming, strcpy is a standard library function used to copy strings but lacks built-in protection against buffer overflows because it does not check if the destination buffer has sufficient space for the source string. When this unsafe function processes data derived from user-controlled inputs without prior length verification, it creates a classic stack-based buffer overflow condition that can be leveraged by an attacker to execute arbitrary code on the target device.
The specific attack vector involves manipulating the HTTP_COOKIE header sent during communication with the web server running lighttpd. The CGI script responsible for exporting ping or trace route data fails to adequately sanitize or limit the length of values contained within cookie headers before passing them to strcpy. By crafting a maliciously sized HTTP_COOKIE value, an attacker can overwrite adjacent memory locations on the stack, including return addresses and saved frame pointers. This manipulation allows for precise control over program execution flow, enabling the injection and execution of shellcode that grants the attacker remote code execution capabilities with the privileges assigned to the web server process, which is often root or a high-privilege user in embedded systems due to historical design oversights.
From an operational impact perspective, this vulnerability poses a severe risk as it can be exploited remotely over the network without requiring any form of authentication if the management interface is exposed to untrusted networks such as the internet. The fact that the exploit has been publicly disclosed significantly increases the likelihood of automated attacks and widespread compromise across vulnerable devices in the wild. Successful exploitation could lead to complete device takeover, allowing attackers to intercept traffic, install persistent backdoors, pivot into internal network segments, or use the compromised router for botnet activities. This scenario aligns with Common Weakness Enumeration (CWE) category CWE-120: Buffer Copy without Checking Size of Input, which is a subset of the broader CWE-787: Out-of-bounds Write vulnerability class. Furthermore, in terms of tactical classification under MITRE ATT&CK for IoT and embedded systems, this flaw facilitates initial access through remote code execution techniques often categorized under T1059 or related command-and-control vectors depending on subsequent actions taken by the adversary post-exploitation.
Mitigation strategies must address both immediate remediation and long-term security hygiene. The primary solution is to apply a firmware update provided by Wavlink that replaces the unsafe strcpy calls with safer alternatives such as strncpy, strlcpy, or snprintf, ensuring that buffer boundaries are strictly respected during string copying operations. Developers should also implement strict input validation routines that check the length of all incoming HTTP headers and parameters before processing them within CGI scripts. For organizations unable to immediately update firmware, network-level controls can provide temporary relief by restricting access to the device's management interface via firewall rules or VLAN segmentation, ensuring it is not directly accessible from untrusted networks like the public internet. Additionally, disabling unnecessary services such as remote telnet or SSH if they are enabled and exposing only essential web interfaces reduces the attack surface available for exploitation of this specific vulnerability vector.