Vulnerability · Published Apr 21, 2026 · Assigned by GitHub_M
CVE-2026-40279BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`
Low 3.7
In plain English
A low-severity security flaw in bacnet-stack from bacnet-stack. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 15% of all known vulnerabilities).
Official 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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| bacnet-stack | bacnet-stack | < 1.4.3 |
Weakness: CWE-758 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L