CVE-2026-40279

BACnet Stack is a BACnet open source protocol stack C library for embedded systems. Prior to 1.4.3, decode_signed32() in src/bacnet/bacint.c reconstructs a 32-bit signed integer from four APDU bytes using signed left shifts. When any of the four bytes has bit 7 set (value ≥ 0x80), the left-shift operation overflows a signed int32_t, which is undefined behavior per the C standard. This is flagged thousands of times per minute by UndefinedBehaviorSanitizer on any BACnet input containing signed-integer property values with high-bit-set bytes. This vulnerability is fixed in 1.4.3.

• CWE-758

• https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxvExploit, Mitigation, Vendor Advisory
• https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxvExploit, Mitigation, Vendor Advisory

Published

Apr 21, 2026

Last Modified

Jun 17, 2026

Status

Analyzed

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