BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`

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Summary

CVECVE-2026-40279
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-21 17:16:54 UTC
Updated2026-04-22 21:24:26 UTC
DescriptionBACnet 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.

Risk And Classification

Primary CVSS: v3.1 3.7 LOW from [email protected]

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

EPSS: 0.000330000 probability, percentile 0.097570000 (date 2026-04-22)

Problem Types: CWE-758 | CWE-758 CWE-758: Reliance on Undefined, Unspecified, or Implementation-Defined Behavior

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary3.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
3.1CNADECLARED3.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Bacnet-stack Bacnet-stack affected < 1.4.3 Not specified

References

ReferenceSourceLinkTags
github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-... 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
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