A stack-based buffer overflow vulnerability in the Tenda AC9 router allows remote attackers to cause a persistent denial of service condition by manipulating specific configuration parameters.

The vulnerability exists in the formGetRebootTimer function, which fails to properly validate the length of the sys.schedulereboot.start_time and sys.schedulereboot.end_time arguments. An authenticated attacker with high privileges can trigger a stack-based buffer overflow, leading to a persistent crash of the web service that survives device reboots.

The exploitation of this vulnerability results in a persistent denial of service for the affected router, rendering the management interface and potentially network services unreachable. Given the CVSS score of 7.2, this represents a high-severity risk to business continuity, particularly for remote branch offices or home-office setups relying on these devices for connectivity. Repeated service crashes can lead to significant operational downtime and necessitate manual recovery efforts.

Immediate Action: As no official patch is currently available, administrators should restrict administrative access to the device management interface to trusted internal networks only.

Proactive Monitoring: Monitor system logs for repeated web service restarts or unexpected device reboots that may indicate exploitation attempts.

Compensating Controls: Implement network-level access control lists (ACLs) to ensure only authorized management workstations can communicate with the Tenda AC9 web interface.

Public Exploit Available: Yes, a public proof-of-concept is available via the researcher's published technical write-up on GitHub.

Due to the availability of proof-of-concept code and the potential for persistent denial of service, this vulnerability poses a credible risk to network stability. Organizations should immediately restrict administrative access to the affected devices and monitor for vendor releases. Until a firmware update is provided, isolating management interfaces is the most effective method to mitigate the risk of remote exploitation.