CVE-2026-40279
BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`
- State
- Published
- Severity
- 3.7 Low
- Published
- Apr 21, 2026
- Updated
- Apr 21, 2026
- Reserved
- Apr 10, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 3.7 Low | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L | GitHub_M |
Weaknesses
- CWE-758 Reliance on Undefined, Unspecified, or Implementation-Defined Behavior
Affected Products
| Product | Versions |
|---|---|
bacnet-stackbacnet-stack |
|
References
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