A flaw in snap7’s TS7Worker::PerformFunctionWrite() routine corrupts heap memory when a specially crafted Modbus packet is processed. This unchecked write to unmanaged memory, identified as CWE-122, can crash the library, leading to loss of availability for any application or device that relies on snap7 for Modbus communication.

The vulnerability exists in the open‑source snap7 library version 1.4.3. Devices or software that incorporate this library—such as industrial automation controllers, SCADA systems, or monitoring tools—are potentially exposed. Later releases of snap7 are expected to contain the fix.

The CVSS score of 7.5 classifies the issue as high severity, although the EPSS score of less than 1% suggests a low current exploitation probability. Based on the description, it is inferred that the attack vector is remote, most likely through the Modbus TCP port, allowing an external actor to trigger the overflow and induce a denial‑of‑service. The vulnerability is not currently listed in the CISA KEV catalog, but its remote nature and impact warrant prompt remediation.