CVE-2026-54410 describes an off-by-one buffer overflow in the recv_msg_header function of the Modbus/TCP server component of debevv nanoMODBUS through version 1.23.0. The vulnerability arises because the function improperly handles the Length field in the MBAP frame, allowing an attacker to write one byte past the allocated 260-byte receive buffer. This can be triggered remotely without authentication by sending a specially crafted MBAP frame with the Length field set to 255. The flaw is categorized under CWE-193 (Off-by-one Error) and CWE-787 (Out-of-bounds Write). No official patch or remediation guidance is currently available from the vendor.

Successful exploitation allows a remote unauthenticated attacker to cause a buffer overflow by writing one byte beyond the buffer boundary. This could lead to memory corruption, potentially resulting in denial of service or other undefined behavior. The CVSS 4.0 score of 7.8 reflects a high severity with low attack complexity and no required privileges or user interaction.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should consider implementing network-level protections such as filtering or blocking untrusted Modbus/TCP traffic to reduce exposure. Monitor vendor channels for updates regarding an official fix.