CVE-2026-41923 Overview
CVE-2026-41923 is an unauthenticated operating system (OS) command injection vulnerability in the WDR201A WiFi Extender (hardware version V2.1, firmware LFMZX28040922V1.02). The flaw resides in the internet.cgi binary, specifically in the set_add_routing function, which concatenates the user-supplied gateway POST parameter into a shell command without sanitization. Attackers can inject arbitrary shell commands that the device executes through popen(), with partial command output reflected in the HTTP response. The weakness is tracked as CWE-78 (Improper Neutralization of Special Elements used in an OS Command).
Critical Impact
Remote unauthenticated attackers can execute arbitrary shell commands on affected WiFi extenders, leading to full device compromise and pivot opportunities into adjacent networks.
Affected Products
- WDR201A WiFi Extender, Hardware Version V2.1
- WDR201A Firmware LFMZX28040922V1.02
- Devices exposing the internet.cgi web interface
Discovery Timeline
- 2026-05-04 - CVE-2026-41923 published to NVD
- 2026-05-05 - Last updated in NVD database
Technical Details for CVE-2026-41923
Vulnerability Analysis
The WDR201A web management interface exposes a routing configuration endpoint handled by the internet.cgi binary. When a client submits a POST request that triggers the set_add_routing function, the handler reads the gateway parameter and embeds it directly into a shell command string. The constructed command is then passed to popen(), which spawns a shell to interpret the input. Because the parameter never passes through input validation or shell metacharacter escaping, attackers can break out of the intended command context using characters such as ;, |, `, or $(). The popen() invocation reads back command output, and a portion of that output is returned in the HTTP response, giving attackers immediate feedback on injected commands.
Root Cause
The root cause is unsafe string concatenation between attacker-controlled input and a shell command template inside set_add_routing. The function trusts the gateway POST parameter, which should contain only an IPv4 address, and does not validate the format or strip shell metacharacters before invoking the shell.
Attack Vector
Exploitation requires only network reachability to the device's HTTP management interface and no authentication. An attacker on the local network, or on the internet if the management interface is exposed, sends a crafted POST request to the routing endpoint with a malicious gateway value containing shell metacharacters followed by arbitrary commands. Commands run with the privileges of the web server process, typically root on embedded SOHO devices, granting full control over the firmware, configuration, and traffic passing through the extender.
No verified public proof-of-concept code is available at this time. For technical details, see the VulnCheck advisory for WDR201A and the GitHub IoT vulnerability disclosure.
Detection Methods for CVE-2026-41923
Indicators of Compromise
- POST requests to internet.cgi containing shell metacharacters (;, |, &, `, $()) within the gateway parameter value.
- Outbound connections from the WiFi extender to unknown external hosts shortly after a routing configuration request.
- Unexpected child processes spawned by the web server, such as wget, curl, tftp, nc, or sh -c invocations.
- Modified or new binaries in writable firmware paths such as /tmp or /var.
Detection Strategies
- Inspect HTTP request bodies destined for the device management interface for non-numeric characters in the gateway field, since legitimate values must be IPv4 addresses.
- Correlate router or extender DNS and outbound traffic logs against known-good firmware update endpoints to flag anomalous callbacks.
- Use signatures that match command injection patterns in application/x-www-form-urlencoded POST bodies referencing routing parameters.
Monitoring Recommendations
- Forward firewall, NetFlow, and DNS telemetry from network segments containing IoT devices into a SIEM such as the SentinelOne Singularity Data Lake for OCSF-normalized analysis and retroactive hunting.
- Alert on management-plane HTTP traffic originating from untrusted VLANs to consumer-grade WiFi extenders.
- Track first-seen process and connection behavior for IoT devices to surface deviations after exploitation.
How to Mitigate CVE-2026-41923
Immediate Actions Required
- Remove WDR201A WiFi Extenders running firmware LFMZX28040922V1.02 from networks where untrusted clients can reach the management interface.
- Block inbound access to the device's HTTP management port from the WAN and from guest or untrusted internal networks.
- Reset device credentials and review router logs for signs of unauthorized routing or DNS changes.
Patch Information
No vendor patch has been published in the referenced advisories at the time of CVE assignment. Operators should monitor the VulnCheck advisory for vendor updates and consider replacing the device with a maintained model if no fix is released.
Workarounds
- Place the WDR201A on an isolated VLAN with no access to corporate or sensitive network segments.
- Restrict management interface access to a single trusted administrative host using firewall rules.
- Disable remote administration features and verify that the device is not reachable from the internet.
- If feasible, decommission the device and replace it with hardware that receives ongoing security updates.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
