# CVE-2026-40279: BACnet Stack is a BACnet open source protocol stack C library for embedded systems. Prior to 1.4.3, decode_signed32()…

Source: https://junglewise.ai/threats/cve-2026-40279-bacnet-stack-is-a-bacnet-open-source-protocol-stack-c-library-for  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-21  
License: CC BY 4.0 with a link back

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.

Technologies: [Bacnetstack Bacnet Stack](https://junglewise.ai/threats/technologies/bacnetstack-bacnet-stack). Vendors: [Bacnetstack](https://junglewise.ai/threats/vendors/bacnetstack).

## Quick answers

**Is CVE-2026-40279 exploited in the wild?** 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.

## Affected products

- Bacnetstack Bacnet Stack

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