CVE-2026-2138: Tenda TX9 Firmware Buffer Overflow Flaw

CVE-2026-2138 Overview

CVE-2026-2138 is a buffer overflow vulnerability affecting Tenda TX9 routers running firmware versions up to 22.03.02.10_multi. The flaw resides in the sub_42D03C function processing requests to the /goform/SetStaticRouteCfg endpoint. Attackers can manipulate the list argument to trigger memory corruption in the router's HTTP service. The vulnerability is exploitable remotely over the network and a public exploit has been disclosed. Successful exploitation can compromise the confidentiality, integrity, and availability of the affected device. The issue is classified under CWE-119 for improper restriction of operations within memory bounds.

Critical Impact
Remote attackers with low privileges can trigger a buffer overflow in the router's web management interface, potentially leading to arbitrary code execution or device compromise.

Affected Products

Tenda TX9 router hardware
Tenda TX9 firmware versions up to 22.03.02.10_multi
Tenda TX9 Pro variants exposing the /goform/SetStaticRouteCfg endpoint

Discovery Timeline

2026-02-08 - CVE-2026-2138 published to NVD
2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-2138

Vulnerability Analysis

The vulnerability exists within the sub_42D03C function of the Tenda TX9 web management binary. This function handles HTTP POST requests to the /goform/SetStaticRouteCfg endpoint, which configures static routing entries on the device. The list parameter supplied in the request is copied into a fixed-size memory buffer without adequate bounds checking. Supplying an oversized value for list overflows adjacent memory regions on the stack or heap. This corruption can overwrite control data such as saved return addresses or function pointers used by the embedded HTTP service. The CWE-119 classification reflects the underlying weakness in memory boundary enforcement common to embedded router firmware.

Root Cause

The root cause is a missing length validation on the list argument passed to sub_42D03C. The handler uses an unsafe string copy operation that trusts attacker-supplied input length. Embedded MIPS or ARM firmware of this class typically lacks modern stack protections such as stack canaries or address space layout randomization, which amplifies the impact of the overflow.

Attack Vector

An attacker reachable over the network can submit a crafted POST request to /goform/SetStaticRouteCfg with an overlong list parameter. The attacker requires low-level authentication to the device's web interface, which is often satisfied by default or weak credentials on consumer routers. Once exploited, the attacker can crash the HTTP service or hijack execution flow to run attacker-controlled code on the device. Public exploit documentation for this issue is available in the GitHub IoT Vulnerability Documentation and tracked in VulDB #344773.

No verified exploit code is reproduced here. Refer to the linked references for technical proof-of-concept details.

Detection Methods for CVE-2026-2138

Indicators of Compromise

HTTP POST requests to /goform/SetStaticRouteCfg containing unusually long list parameter values
Unexpected reboots or crashes of the Tenda TX9 web administration service
Outbound connections from the router to unknown command-and-control infrastructure following administrative configuration changes
New or modified static route entries not initiated by an administrator

Detection Strategies

Inspect network traffic for HTTP requests targeting /goform/SetStaticRouteCfg and flag payloads exceeding expected parameter lengths
Deploy intrusion detection signatures that match anomalous request sizes to Tenda router management endpoints
Correlate router log entries for repeated authentication attempts followed by configuration POSTs to routing endpoints
Monitor for buffer overflow patterns such as long sequences of repeated characters or shellcode markers in HTTP request bodies

Monitoring Recommendations

Restrict and log access to the router's web management interface from the LAN and disable WAN-side management
Forward router syslog data to a centralized log platform for behavioral analysis
Alert on unauthorized changes to static routing tables and DNS settings
Track firmware version inventory across deployed Tenda devices to identify vulnerable units

How to Mitigate CVE-2026-2138

Immediate Actions Required

Disable remote (WAN) administration on all Tenda TX9 devices until a patch is applied
Restrict LAN-side access to the router management interface to trusted administrative hosts only
Rotate administrative credentials and enforce strong, unique passwords to reduce the value of the low-privilege precondition
Segment vulnerable routers from sensitive network zones using firewall ACLs

Patch Information

No vendor patch has been published in the references available for CVE-2026-2138. Monitor the Tenda Official Website for firmware updates addressing the sub_42D03C handler in /goform/SetStaticRouteCfg. Apply any released firmware update for the TX9 product line as soon as it becomes available and verify the running version against vendor advisories.

Workarounds

Block external access to the router's HTTP management port at the perimeter firewall or ISP gateway
Place the router behind a separate hardened gateway if it must remain in service
Replace end-of-life Tenda TX9 units with supported hardware that receives active security maintenance
Disable static route configuration features for non-administrative users where the firmware permits

bash

# Example: restrict access to the Tenda router management interface using iptables on an upstream Linux gateway
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -s <admin_workstation_ip> -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -s <admin_workstation_ip> -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -j DROP