OpenPLCv3 contains a heap-based buffer overflow in the getData() function in webserver/core/modbusmaster.cpp. getData() reads characters between two delimiters into a caller-supplied buffer with no size parameter and no bounds check. In parseConfig() the function is invoked with the 100-byte heap-allocated MBdevice.devname field. An authenticated attacker with access to the OpenPLC web interface can send a crafted HTTP POST to the /modbus endpoint with an oversized devicename value; the value is persisted to mbconfig.cfg and parsed on load, overflowing devname and overwriting adjacent struct fields (protocol at offset 108, devaddress at offset 109, ipport at offset 210). A 200-byte payload writes 100 bytes past the allocation. The result is heap corruption leading to runtime crash and denial of service of the PLC process control loop, with attacker-controlled overwrite of adjacent configuration fields. The upstream repository was archived on 2026-04-04 and no fix is expected; the vendor has confirmed the issue does not affect OpenPLC Runtime v4.

OpenPLCV3 is vulnerable to an Initialization of a Resource with an Insecure Default vulnerability which could allow an attacker to gain access to the system by bypassing authentication via an API.

OpenPLCV3 REST API endpoint checks for JWT presence but never verifies the caller's role. Any authenticated user with role=user can delete any other user, including administrators, by specifying their user ID or they can create new accounts with role=admin, escalating to full administrator access.

OpenPLCV3 is vulnerable to a Plaintext Storage of a Password vulnerability that could allow an attacker to retrieve credentials and access sensitive information.

OpenPLCV3 is vulnerable to a cross-site request forgery (CSRF) attack due to the absence of proper CSRF validation. This issue allows an unauthenticated attacker to trick a logged-in administrator into visiting a maliciously crafted link, potentially enabling unauthorized modification of PLC settings or the upload of malicious programs which could lead to significant disruption or damage to connected systems.