CVE-2026-11557: Tenda F451 Buffer Overflow Vulnerability

CVE-2026-11557 Overview

CVE-2026-11557 is a stack-based buffer overflow vulnerability in the Tenda F451 router firmware versions 1.0.0.7 and 1.0.0.9. The flaw resides in the fromNatlimit function within /goform/Natlimit, part of the device's Web Management Interface. Attackers can exploit the vulnerability by manipulating the page argument to corrupt stack memory. The attack is performed remotely over the network and requires low privileges. Public exploit code has been disclosed, increasing the likelihood of opportunistic attacks against exposed devices. The vulnerability is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Critical Impact

Remote attackers with low-privilege access can trigger a stack-based buffer overflow in the Tenda F451 web interface, potentially leading to arbitrary code execution or device compromise.

Affected Products

• Tenda F451 firmware version 1.0.0.7
• Tenda F451 firmware version 1.0.0.9
• Tenda F451 Web Management Interface (/goform/Natlimit endpoint)

Discovery Timeline

• 2026-06-08 - CVE-2026-11557 published to NVD
• 2026-06-09 - Last updated in NVD database

Technical Details for CVE-2026-11557

Vulnerability Analysis

The vulnerability exists in the fromNatlimit function, which handles NAT limit configuration requests submitted through the /goform/Natlimit endpoint of the Tenda F451 Web Management Interface. The function processes the user-supplied page parameter without enforcing proper bounds checking before copying the input into a fixed-size stack buffer. This omission allows attacker-controlled data to overwrite adjacent stack memory, including saved return addresses and local variables. Successful exploitation can divert execution flow on the embedded device, leading to arbitrary code execution within the router's firmware context. The defect is consistent with classic embedded web server input handling flaws documented under [CWE-119].

Root Cause

The root cause is missing length validation on the page argument before it is written into a stack-allocated buffer inside fromNatlimit. The handler trusts attacker-supplied HTTP request parameters and uses unsafe string copy operations against a buffer of fixed size. Because the firmware lacks modern memory protection mitigations such as reliable stack canaries or address space layout randomization, the overflow translates directly into reliable control over execution flow.

Attack Vector

An authenticated attacker with low-privilege credentials sends a crafted HTTP POST request to /goform/Natlimit containing an oversized page parameter. The malformed request reaches fromNatlimit, where the unchecked copy corrupts the stack frame. Routers exposed to untrusted networks or to attackers with stolen or default credentials are at the greatest risk. A public proof of concept has been published in the GitHub IoT Vulnerability Report, removing a barrier to exploitation.

Detection Methods for CVE-2026-11557

Indicators of Compromise

• HTTP POST requests to /goform/Natlimit containing abnormally long page parameter values
• Unexpected reboots, crashes, or watchdog resets of the Tenda F451 device following web interface activity
• New or unexplained outbound connections initiated by the router to untrusted hosts
• Web management interface authentication attempts originating from unfamiliar IP addresses

Detection Strategies

• Inspect HTTP traffic destined for router management interfaces for oversized parameters targeting /goform/ endpoints
• Deploy IDS or IPS signatures that flag long page argument values posted to Tenda goform URIs
• Correlate router crash logs and syslog messages with preceding web management requests to identify exploitation attempts

Monitoring Recommendations

• Forward router syslog and authentication events to a centralized SIEM for analysis
• Alert on management interface access from outside trusted administrative subnets
• Monitor for repeated POST requests to /goform/Natlimit from a single source within short time windows

How to Mitigate CVE-2026-11557

Immediate Actions Required

• Restrict access to the Tenda F451 Web Management Interface to trusted internal networks only and disable WAN-side administration
• Rotate all router administrator credentials and disable any default or shared accounts
• Audit existing devices for signs of compromise, including unexpected configuration changes to NAT or firewall rules
• Place affected devices behind a network segmentation boundary until a vendor patch is applied

Patch Information

No official vendor patch has been published in the referenced advisories at the time of disclosure. Administrators should monitor the Tenda Official Website and the VulDB CVE-2026-11557 entry for firmware updates addressing the fromNatlimit function.

Workarounds

• Disable remote management of the router over WAN interfaces and limit HTTP access to wired LAN administrators
• Apply ACLs on upstream firewalls to block inbound traffic to TCP ports used by the router web interface
• Replace end-of-support Tenda F451 devices with hardware that receives active firmware maintenance
• Enforce strong, unique administrator passwords to reduce the likelihood of low-privilege exploitation

# Example firewall rule to restrict access to the router management interface
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP