CVE-2026-40279

LOW

BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`

Title source: cna
STIX 2.1

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.

References (1)

Core 1
Core References

Scores

CVSS v3 3.7
EPSS 0.0024
EPSS Percentile 15.1%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

CISA SSVC

Vulnrichment
Exploitation poc
Automatable no
Technical Impact partial

Details

CWE
CWE-758
Status published
Products (2)
bacnet-stack/bacnet-stack < 1.4.3
bacnetstack/bacnet_stack < 1.4.3
Published Apr 21, 2026
Tracked Since Apr 21, 2026