CVE-2026-21870: Bacnetstack Bacnet Stack

Medium severity, CVSS 5.5. EPSS: 0.3% chance of exploitation in the next 30 days.

BACnet Protocol Stack library provides a BACnet application layer, network layer and media access (MAC) layer communications services. In 1.4.2, 1.5.0.rc2, and earlier, an off-by-one stack-based buffer overflow in the ubasic interpreter causes a crash (SIGABRT) when processing string literals longer than the buffer limit. The tokenizer_string function in src/bacnet/basic/program/ubasic/tokenizer.c incorrectly handles null termination for maximum-length strings. It writes a null byte to dest[40] when the buffer size is only 40 (indices 0-39), triggering a stack overflow.

Affected products

• Bacnetstack Bacnet Stack: up to and including 1.4.2; version 1.5.0 only

Published 2026-02-13. Last modified 2026-06-17.