github.comConfirmation
https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv CVE-2026-40279
LOW
BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`
Record summary
CVE-2026-40279 has a selected CVSS score of 3.7 (low).
Description
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.
Description source: CVE List
Exploitation context
CISA SSVC decision
ExploitationPoC
AutomatableNo
Technical impactPartial
CISA Coordinator · SSVC 2.0.3 · Evaluated Apr 21, 2026 · Source: CVE List
Affected products and versions
1| Product | Source | Version range | Status |
|---|---|---|---|
bacnet-stackBrowse bacnet-stack / bacnet-stack | CVE List | < 1.4.3 | affected |