VDB-358520 · CVE-2026-40279 · GHSA-326g-j95f-gmxv

bacnet-stack BACnet Stack up to 1.4.2 src/bacnet/bacint.c decode_signed32 reliance on undefined, unspecified, or implementation-defined behavior

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
3.7	$0-$5k	3.27

Summaryinfo

A vulnerability categorized as problematic has been discovered in bacnet-stack BACnet Stack up to 1.4.2. This affects the function decode_signed32 of the file src/bacnet/bacint.c. Such manipulation leads to reliance on undefined, unspecified, or implementation-defined behavior. This vulnerability is referenced as CVE-2026-40279. It is possible to launch the attack remotely. No exploit is available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in bacnet-stack BACnet Stack up to 1.4.2 and classified as problematic. Affected by this issue is the function decode_signed32 of the file src/bacnet/bacint.c. The manipulation with an unknown input leads to a reliance on undefined, unspecified, or implementation-defined behavior vulnerability. Using CWE to declare the problem leads to CWE-758. The product uses an API function, data structure, or other entity in a way that relies on properties that are not always guaranteed to hold for that entity. Impacted is availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-40279 since 04/10/2026. The exploitation is known to be difficult. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available.

Upgrading to version 1.4.3 eliminates this vulnerability.

VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Vendor

bacnet-stack

Name

BACnet Stack

Version

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 3.7
VulDB Meta Temp Score: 3.7

VulDB Base Score: 3.7
VulDB Temp Score: 3.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 3.7
CNA Vector (GitHub_M): 🔒

CVSSv2info

AV	AC	Au	C	I	A
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💳	💳	💳	💳	💳	💳
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Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Reliance on undefined, unspecified, or implementation-defined behavior
CWE: CWE-758
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: BACnet Stack 1.4.3

Timelineinfo

04/10/2026 CVE reserved
04/21/2026 +11 days Advisory disclosed
04/21/2026 +0 days VulDB entry created
04/21/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: GHSA-326g-j95f-gmxv
Status: Confirmed

CVE: CVE-2026-40279 (🔒)
GCVE (CVE): GCVE-0-2026-40279
GCVE (VulDB): GCVE-100-358520

Entryinfo

Created: 04/21/2026 19:25
Changes: 04/21/2026 19:25 (65)
Complete: 🔍
Cache ID: 216::103