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CVE-2026-40279 Details

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.

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: [email protected]CVSS-B:3.7 LOWVector:CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv	CISA-ADP	ExploitMitigationVendor Advisory
https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv	[email protected]	ExploitMitigationVendor Advisory

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-758	Reliance on Undefined, Unspecified, or Implementation-Defined Behavior	[email protected]

Affected Products

Product	Versions
bacnetstack bacnet stack	< 1.4.3
CPE cpe:2.3:a:bacnetstack:bacnet_stack:::::::: Remediation No remediation found in references.

Change History

5 change records found show changes

Date	Action	Recorded By
Jun 17, 2026	CVE Modified	[email protected]
Jun 17, 2026	CVE Modified	CISA-ADP
Apr 27, 2026	Initial Analysis	[email protected]
Apr 21, 2026	CVE Modified	CISA-ADP
Apr 21, 2026	New CVE Received	[email protected]