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CVE-2026-40279— BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`

Quick assessment

Affected
bacnet-stack bacnet-stack
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

BACnet Stack是BACnet Stack开源的一个适用于嵌入式系统、Linux、MacOS、BSD 和 Windows 的 BACnet 开源协议栈 C 库。 BACnet Stack 1.4.3之前版本存在安全漏洞，该漏洞源于src/bacnet/bacint.c中的decode_signed32函数使用有符号左移从四个APDU字节重构32位有符号整数时，当任何字节的第7位被设置时，左移操作会导致有符号int32_t溢出，这是未定义行为。

CVSS 3.7 · Low EPSS 0.33% · P24

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-40279

Vulnerability Information
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Vulnerability Title
BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
依赖未定义、未指明或实现定义的行为
Source: CVE Program / CVE List V5
Vulnerability Title
BACnet Stack 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
BACnet Stack是BACnet Stack开源的一个适用于嵌入式系统、Linux、MacOS、BSD 和 Windows 的 BACnet 开源协议栈 C 库。 BACnet Stack 1.4.3之前版本存在安全漏洞，该漏洞源于src/bacnet/bacint.c中的decode_signed32函数使用有符号左移从四个APDU字节重构32位有符号整数时，当任何字节的第7位被设置时，左移操作会导致有符号int32_t溢出，这是未定义行为。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
bacnet-stack bacnet-stack < 1.4.3 -

II. Public POCs for CVE-2026-40279

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III. Intelligence Information for CVE-2026-40279

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Vendor Advisories for CVE-2026-40279 (1)

IV. Related Vulnerabilities

Same product: bacnet-stack
Same vendor: bacnet-stack
Same weakness: CWE-758

V. Comments for CVE-2026-40279

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