A critical stack-based buffer overflow in Tenda CX12L routers allows unauthenticated remote attackers to execute arbitrary code or crash the device.

The vulnerability exists in the fromNatStaticSetting function within the /goform/NatStaticSetting endpoint, where the page parameter is processed using an unsafe sprintf call without length validation. This allows an unauthenticated attacker to supply an oversized input that overflows a 256-byte stack buffer, resulting in memory corruption or remote code execution.

Successful exploitation of this vulnerability poses a severe risk to network infrastructure. By gaining unauthorized access or control over the router, an attacker could intercept sensitive network traffic, modify configuration settings to facilitate man-in-the-middle attacks, or use the device as a pivot point to compromise internal network assets. Given the high CVSS score of 8.8, this flaw represents a significant threat to organizational data confidentiality and operational integrity.

Immediate Action: Update the Tenda CX12L firmware to the latest available version provided by the vendor, which includes the necessary bounds checking to prevent buffer overflow.

Proactive Monitoring: Monitor network traffic for anomalous POST requests directed at the /goform/NatStaticSetting endpoint, particularly those containing excessively large payloads.

Compensating Controls: Deploy a Web Application Firewall (WAF) or an Intrusion Prevention System (IPS) rule to block or sanitize incoming HTTP requests that contain oversized parameters directed at the vulnerable management URI.

Public Exploit Available: Yes — as documented in the researcher's technical write-up on GitHub.

The vulnerability is severe and requires immediate attention due to the potential for unauthenticated remote code execution. Administrators should prioritize patching affected Tenda CX12L devices immediately. If an update cannot be applied instantly, isolate the management interface from the public internet to mitigate the risk of remote exploitation.