CVE-2026-110958: Wavlink WN530HG4B Buffer Overflow Flaw

CVE-2026-110958 Overview

CVE-2026-110958 is a heap-based buffer overflow [CWE-119] affecting the Wavlink WN530HG4B router running firmware M30HG4B_V260724. The flaw resides in an unspecified function within api.cgi and is reachable over the network without authentication or user interaction. A remote attacker can trigger memory corruption by manipulating input to the vulnerable handler. The vendor has confirmed the issue and shipped a fix in firmware build 2026-09-24-841a51c6d5_tclinux.bin. According to the vendor, the api=info&client=app handler no longer builds a shell command; it invokes the login script through an argument vector using execvp instead of system(), and the client address is length-limited and null-checked. A public exploit exists, raising the risk of opportunistic exploitation.

Critical Impact
Unauthenticated remote attackers can corrupt heap memory in api.cgi, potentially achieving code execution on affected Wavlink WN530HG4B devices.

Affected Products

Wavlink WN530HG4B router
Firmware version M30HG4B_V260724
Devices sharing the vulnerable api.cgi handler prior to build 2026-09-24-841a51c6d5_tclinux.bin

Discovery Timeline

2026-10-15 - CVE-2026-110958 published to NVD
2026-10-15 - Last updated in NVD database

Technical Details for CVE-2026-110958

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow [CWE-119] in api.cgi, the HTTP management interface on the Wavlink WN530HG4B. An attacker-supplied value passed into the api=info&client=app handler is written into a heap buffer without proper length validation. Memory corruption occurs when the input exceeds the allocated buffer boundaries. Because the handler originally passed the client-controlled address directly into a shell command built with system(), the fix also removes a command injection pathway alongside the overflow.

The vendor confirmed the finding and documented the remediation: the login script is now invoked through an argument vector with execvp, and the client address is both length-limited and null-checked. These changes prevent the oversized or malformed input from reaching the vulnerable code path.

Root Cause

The root cause is missing bounds checking and improper validation of the client parameter processed by api.cgi. The handler assumed a bounded, null-terminated client address string and copied it into a fixed-size heap buffer. No length check and no null check were performed before use, allowing adjacent heap metadata and allocations to be overwritten.

Attack Vector

Exploitation requires only network access to the device's HTTP interface. The attacker sends a crafted request to api.cgi targeting the info API with a malicious client=app payload containing an oversized address value. No authentication, privileges, or user interaction are needed. A proof-of-concept has been published, and references to the exploit are tracked in the VulDB CVE-2026-110958 entry.

No verified exploit code is reproduced here. Technical details are available in the VulDB Vulnerability #420571 record.

Detection Methods for CVE-2026-110958

Indicators of Compromise

HTTP requests to api.cgi containing api=info&client=app with unusually long or non-ASCII client values
Unexpected process launches or child shells spawned by the router's web daemon
Device crashes, reboots, or watchdog resets correlated with inbound requests to the management interface
New or modified firmware images not matching the vendor-published build 2026-09-24-841a51c6d5_tclinux.bin

Detection Strategies

Inspect HTTP traffic to the router management plane for api.cgi requests with oversized client parameters that exceed expected address lengths
Alert on api.cgi requests originating from untrusted network segments or external interfaces
Monitor router syslog for abnormal termination of the web service or recurring process restarts
Verify running firmware version against the fixed build published on the Wavlink Firmware Update portal

Monitoring Recommendations

Capture and retain network metadata for all administrative interfaces of edge devices to support retroactive hunting
Enable centralized logging from affected routers and forward events to a SIEM or data lake for correlation
Baseline normal api.cgi request patterns and alert on deviations in parameter length or frequency

How to Mitigate CVE-2026-110958

Immediate Actions Required

Upgrade affected Wavlink WN530HG4B devices to firmware 2026-09-24-841a51c6d5_tclinux.bin or later
Restrict access to the router web management interface so it is reachable only from trusted internal networks
Disable remote (WAN-side) administration if it is not required for operations
Review device logs for prior requests to api.cgi with suspicious client parameters

Patch Information

Wavlink has published a fixed firmware image. The remediated handler uses execvp with an argument vector instead of system(), and the client address is length-limited and null-checked. Download the update from the Wavlink Firmware Update link referenced in the advisory. Additional details are available at VulDB CVE-2026-110958.

Workarounds

Place the device behind a network firewall and block inbound HTTP/HTTPS to the management interface from untrusted sources
Apply ACLs on the router to limit api.cgi access to a specific administrative subnet or jump host
Segment IoT and network infrastructure devices from general user and server VLANs to limit lateral exposure
Decommission or replace devices that cannot be updated to the fixed firmware build

bash

# Example: restrict management interface access with iptables on an upstream gateway
iptables -A FORWARD -p tcp -d <router_ip> --dport 80  -s <admin_subnet> -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -s <admin_subnet> -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 80  -j DROP
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -j DROP