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8.7
CVE-2026-11826: OpenPLC_v3: Modbus Master Denial of Service via Heap Corruption
CVE-2026-11826
CVE-2026-11826
Summary
OpenPLC_v3, a software used for process control, has a security flaw that allows an attacker to crash the system and disrupt its operation. This issue affects the web interface and can be exploited by an authenticated attacker. The vendor has confirmed that OpenPLC Runtime v4 is not affected, but no fix is available for OpenPLC_v3 due to its archived repository.
What to do
No fix is available yet. Check with your software vendor for updates.
Affected software
| Vendor | Product | Affected versions |
|---|---|---|
| openplcproject | openplc_v3 | <= b470206 |
Original title
OpenPLC_v3 Heap-Based Buffer Overflow in Modbus Master getData()
Original description
OpenPLC_v3 contains a heap-based buffer overflow in the getData() function in webserver/core/modbus_master.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 MB_device.dev_name field. An authenticated attacker with access to the OpenPLC web interface can send a crafted HTTP POST to the /modbus endpoint with an oversized device_name value; the value is persisted to mbconfig.cfg and parsed on load, overflowing dev_name and overwriting adjacent struct fields (protocol at offset 108, dev_address at offset 109, ip_port 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.
nvd CVSS3.1
8.8
nvd CVSS4.0
8.7
Vulnerability type
CWE-122
Heap-based Buffer Overflow
Published: 18 Jul 2026 · Updated: 20 Jul 2026 · First seen: 18 Jul 2026