CVE-2026-40279

low

Published 2026-04-21 · Modified 2026-04-27

CVSS v3

3.7

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS v2

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VIR risk

3.7

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.

Predictions

Exploit likelihood

47%

Patch ETA

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Heuristic predictions, AS-IS, for prioritization only.

Mitigations

vendor Authored 2026-05-27

Vendor advisory: security-advisories@github.com — https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv

Application impact

Vendor	Product	Versions	Fixed
bacnetstack	bacnet_stack	`{"endExcluding":"1.4.3"}`	`1.4.3`

References

CWEs

CWE-758

Verify integrity in audit chain (admin only). AS-IS.