A critical stack-based buffer overflow in Tenda A21 routers allows remote attackers to execute arbitrary code, posing a significant risk to network integrity.

The vulnerability exists within the setSchedWifi function of the /goform/openSchedWifi endpoint. By manipulating the schedStartTime or schedEndTime arguments, an authenticated attacker can trigger a stack-based buffer overflow, resulting in memory corruption.

The ability for a remote attacker to trigger a buffer overflow in networking hardware can lead to full system compromise, including unauthorized administrative control and persistent access. With a CVSS score of 8.8, this vulnerability represents a high risk to business operations, potentially facilitating lateral movement into protected internal segments and the exfiltration of sensitive traffic.

Immediate Action: As no official patch is currently available, administrators should immediately restrict access to the management interface of the Tenda A21 to trusted internal IP addresses only.

Proactive Monitoring: Security teams should monitor network traffic for anomalous HTTP POST requests directed at the /goform/openSchedWifi endpoint, particularly those containing unusually long string values.

Compensating Controls: Deploying a Web Application Firewall or an Intrusion Prevention System with custom rules to inspect and filter inputs to the affected endpoint can provide effective virtual patching until the vendor releases a firmware update.

Public Exploit Available: Yes, a public proof-of-concept is available via the referenced GitHub issue tracker.

Given the severity of this memory corruption flaw and the availability of a public proof-of-concept, users must treat this as a high-priority issue. Administrators should isolate the device from the public internet immediately and monitor vendor channels closely for the release of a security firmware update.