CVE-2026-71936 in VigorSwitch G2540xs
Summary
by MITRE • 08/24/2026
Multiple DrayTek VigorSwitch models contain a buffer overflow vulnerability in the sysreboot function. The vulnerability is caused by unsafe concatenation of split valueN data into a fixed-size buffer. 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 identified vulnerability resides within the sysreboot function of multiple DrayTek VigorSwitch models and represents a classic buffer overflow condition arising from improper input validation during string manipulation operations. The core technical flaw involves the unsafe concatenation of split valueN data into a fixed-size memory buffer without adequate bounds checking or length verification prior to the copy operation. When an attacker supplies crafted input that exceeds the allocated buffer capacity, the excess data overwrites adjacent memory locations on the stack or heap, leading to memory corruption. This specific implementation error allows for potential control flow hijacking if the overwritten return address or function pointer can be precisely manipulated, although in many embedded network device contexts, such flaws are primarily exploited to cause a denial of service by crashing the management process or the entire system firmware due to segmentation faults and subsequent watchdog resets.
From an operational perspective, this vulnerability poses significant risks to the availability and integrity of network infrastructure components managed by these switches. While the immediate impact is often observed as a device reboot or unavailability of the web management interface, the potential for arbitrary code execution cannot be dismissed entirely given the nature of buffer overflows in C-based embedded systems. If an attacker successfully exploits this flaw to execute remote commands, they could gain full administrative control over the switch, enabling them to intercept network traffic, modify routing tables, or use the device as a pivot point for further attacks within the internal network segment. The requirement for valid administrative credentials significantly mitigates the risk of widespread automated exploitation but does not eliminate threats from insider actors or compromised management stations that possess legitimate access privileges.
This vulnerability aligns with Common Weakness Enumeration (CWE) categories such as CWE-120, Buffer Copy without Checking Size of Input, and potentially CWE-787, Out-of-bounds Write, depending on the specific memory layout and overwrite targets within the device firmware. In terms of tactical classification under the MITRE ATT&CK framework for Enterprise or ICS, this flaw facilitates Initial Access through valid accounts (T1078) followed by potential Execution capabilities if code execution is achieved, though it primarily serves as a Denial of Service vector in its current known exploitation scenarios. The lack of input sanitization highlights deficiencies in secure coding practices during the development phase of embedded network equipment firmware.
To mitigate this vulnerability and reduce the attack surface associated with administrative interfaces, organizations should ensure that all DrayTek VigorSwitch models are updated to the latest firmware versions released by the vendor, which typically include patches for such memory safety issues. Access control measures must be strictly enforced; administrators should restrict access to the web management interface using firewall rules or VLAN segmentation so that only trusted IP addresses can reach the administrative ports. Additionally, changing default credentials and implementing strong password policies reduces the likelihood of credential compromise, thereby limiting the pool of potential attackers who meet the prerequisite for valid authentication. Regular vulnerability assessments focused on network device firmware versions are recommended to maintain visibility over such security defects across the infrastructure estate.