CVE-2026-40279: BACnet Stack is a BACnet open source protocol stack C library for embedded systems. Prior to 1.4.3, decode_signed32()…
CVE-2026-40279 · Severity: low · CVSS 3.7 · Published 2026-04-21
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.
No. Junglewise Threat Intelligence has no report of CVE-2026-40279 being exploited in the wild.
How severe is CVE-2026-40279?
Low severity, with a CVSS score of 3.7, published 21 April 2026.
Which products and versions are affected?
Bacnetstack Bacnet Stack. The advisory does not name versions.
Is there a fix for CVE-2026-40279?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
Am I affected by CVE-2026-40279?
Check whether you run Bacnetstack Bacnet Stack. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.