CVE-2026-71911 in VigorAP 918R
Summary
by MITRE • 08/24/2026
Multiple DrayTek VigorAP models contain a buffer overflow vulnerability in the setLan function. The vulnerability is caused by missing length checks during memory copy operations involving the lanVlanId0, lanIp, and lanNetmask fields. A remote attacker can trigger this vulnerability via crafted input, causing a denial of service or potentially executing arbitrary commands. Exploitation requires valid administrative credentials for the device's web management interface.
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Analysis
by VulDB Data Team • 08/24/2026
The DrayTek VigorAP series of wireless access points contains a critical buffer overflow vulnerability within its network configuration handling logic, specifically located in the setLan function responsible for managing Local Area Network parameters. This flaw stems from insufficient validation of input data lengths during memory copy operations involving three specific fields: lanVlanId0, lanIp, and lanNetmask. When these fields are processed by the device's firmware, there is a lack of rigorous boundary checking to ensure that incoming data does not exceed the allocated buffer size. This architectural weakness allows for an out-of-bounds write condition if maliciously crafted input exceeds the expected limits, leading to memory corruption within the application stack or heap depending on the specific implementation details of the underlying C code structure.
From a technical perspective, this vulnerability is classified under CWE-120, which denotes Buffer Copy without Checking Size of Input Classic buffer overflow. The absence of proper length checks means that an attacker can overwrite adjacent memory locations with arbitrary data. In embedded systems like network access points, such overwrites often target return addresses or function pointers stored on the stack. By carefully crafting the payload to include shellcode and precise offsets for these overwritten values, a remote actor can hijack the control flow of the application. This capability transforms what might otherwise be a simple denial-of-service condition into a full remote code execution scenario, allowing complete compromise of the device's operating environment.
The operational impact of this vulnerability is severe due to its potential to disrupt network infrastructure and facilitate lateral movement within an enterprise or home network. If exploited for denial of service, the buffer overflow can crash the web management interface or the entire firmware process running on the access point, resulting in a loss of connectivity for all devices associated with that specific VigorAP unit. However, the more critical risk is remote code execution. An attacker who successfully exploits this flaw gains the ability to run arbitrary commands with the privileges of the compromised service account. Given that these devices often serve as gateways or central points for network traffic, compromising them can lead to interception of sensitive data, manipulation of routing tables, and use of the device as a pivot point for further attacks against internal assets.
It is important to note that exploitation of this vulnerability requires valid administrative credentials for the device's web management interface. This constraint places the attack within the context of authenticated remote access rather than unauthenticated network-based exploits. Consequently, while the technical severity remains high due to the potential for code execution, the practical risk is mitigated by strong authentication practices such as complex passwords and multi-factor authentication if supported. Nevertheless, the presence of this flaw indicates a significant lapse in secure coding standards during firmware development, highlighting the need for rigorous input validation mechanisms in all network-facing administrative interfaces.
To mitigate this vulnerability, administrators should immediately apply any available firmware updates provided by DrayTek that address these specific memory safety issues. Until patches are applied or if no patch is available, it is crucial to restrict access to the web management interface through strict firewall rules and IP whitelisting, ensuring only trusted administrative workstations can reach the device's configuration pages. Additionally, changing default credentials and enforcing strong password policies reduces the likelihood of an attacker obtaining the necessary authentication tokens required to trigger this exploit. Long-term remediation involves adopting secure development lifecycle practices that include static code analysis tools capable of detecting buffer overflow conditions before deployment, as well as implementing runtime protection mechanisms such as stack canaries or address space layout randomization where supported by the hardware architecture. This incident underscores the importance of treating administrative interfaces with the same security rigor as public-facing services, given their elevated privilege levels and direct impact on network integrity.