CVE-2026-6196: Tenda F456 Buffer Overflow Vulnerability

CVE-2026-6196 Overview

CVE-2026-6196 is a stack-based buffer overflow [CWE-119] in the Tenda F456 router running firmware version 1.0.0.5. The flaw resides in the fromexeCommand function handling requests to the /goform/exeCommand endpoint. Attackers manipulate the cmdinput argument to overflow a fixed-size stack buffer. The issue is remotely exploitable across the network and a public proof-of-concept has been published. Successful exploitation can corrupt the call stack, crash the device, or enable arbitrary code execution on the embedded Linux platform.

Critical Impact

Remote attackers with low-privileged access can trigger memory corruption on Tenda F456 routers, leading to denial of service or potential code execution on the device.

Affected Products

• Tenda F456 router
• Firmware version 1.0.0.5
• /goform/exeCommand web management interface

Discovery Timeline

• 2026-04-13 - CVE-2026-6196 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-6196

Vulnerability Analysis

The vulnerability exists in the fromexeCommand handler exposed through the router's web management endpoint at /goform/exeCommand. The handler reads the cmdinput HTTP parameter and copies its contents into a fixed-size stack buffer without bounds validation. Supplying an oversized cmdinput value overwrites adjacent stack memory, including saved return addresses and frame pointers.

The weakness is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). Tenda's /goform/ handlers are implemented as native C functions in the HTTP daemon, which lacks stack canaries and address space layout randomization (ASLR) on most consumer firmware builds. This significantly increases the reliability of exploitation.

Root Cause

The root cause is the absence of length validation on the user-supplied cmdinput parameter before it is copied into a stack-allocated buffer. Standard unsafe string operations such as strcpy or sprintf are typically responsible for this class of buffer overflow in MIPS and ARM-based Tenda firmware.

Attack Vector

An authenticated remote attacker sends a crafted HTTP POST request to /goform/exeCommand with an oversized cmdinput parameter. The overflow corrupts the stack frame of fromexeCommand, allowing the attacker to redirect execution flow. Because the management interface is reachable over the LAN and, in some deployments, the WAN, attackers can reach the vulnerable endpoint without local access.

The vulnerability manifests when the HTTP request handler processes the cmdinput argument without enforcing a maximum length. See the GitHub PoC Repository for the published exploitation steps and VulDB #357118 for the vulnerability metadata.

Detection Methods for CVE-2026-6196

Indicators of Compromise

• HTTP POST requests to /goform/exeCommand containing unusually long cmdinput parameter values
• Unexpected reboots or httpd process crashes on the Tenda F456 router
• Outbound connections from the router to unfamiliar hosts following management interface activity
• New or modified entries in router system logs referencing fromexeCommand

Detection Strategies

• Inspect inbound HTTP traffic to the router with intrusion detection signatures matching long cmdinput request bodies destined for /goform/exeCommand
• Baseline normal request sizes for /goform/ endpoints and alert on payloads exceeding several hundred bytes
• Correlate router crash events with preceding HTTP requests against the management interface

Monitoring Recommendations

• Forward router syslog data to a centralized log platform and alert on repeated httpd restarts
• Restrict and monitor administrative access to the router's web UI via firewall rules
• Track WAN-side access attempts to TCP/80 and TCP/443 on the router and alert on any non-administrative source IP

How to Mitigate CVE-2026-6196

Immediate Actions Required

• Disable remote (WAN-side) management of the Tenda F456 web interface
• Restrict LAN access to the router's administrative interface to a dedicated management VLAN or trusted hosts
• Rotate the router administrator password and enforce strong credentials
• Monitor Tenda's official site for an updated firmware release addressing CVE-2026-6196

Patch Information

At the time of publication, no vendor patch has been referenced in the NVD entry for CVE-2026-6196. Tenda has not published a security advisory specific to this issue. Administrators should track Tenda Official Site for firmware updates superseding version 1.0.0.5 and apply them as soon as they are available.

Workarounds

• Place the F456 behind a perimeter firewall and block external access to TCP/80 and TCP/443 on the device
• Segment the router management interface from general user networks using VLANs and ACLs
• Replace the device with a supported model if a vendor patch is not released in a reasonable timeframe

# Example firewall rule to block WAN access to the router web UI
iptables -A INPUT -i wan0 -p tcp --dport 80 -j DROP
iptables -A INPUT -i wan0 -p tcp --dport 443 -j DROP