# CVE-2026-40279

## Summary

- **CVE ID:** CVE-2026-40279
- **Severity:** LOW
- **CVSS Score:** 3.7 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L)
- **CWE:** CWE-758
- **Published:** Apr 21, 2026
- **Last Modified:** Apr 21, 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.

## Affected Products

- bacnet-stack — bacnet-stack (< 1.4.3)

## References

- [CNA](https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.24%
- **EPSS Percentile:** 15.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._