Cyber Resilience

CVE-2026-40279

Bacnetstack Bacnet Stack ≤ 1.4.3

Public PoC
Published
21 April 2026
Modified
27 April 2026
Patch / advisory
View advisory
CVSS Score v3.1 3.7
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
EPSS Score 0.0024 16th percentile
Risk Priority 31 floored blend · peak EPSS

Summary

CVE-2026-40279 is a low-severity Reliance on Undefined, Unspecified, or Implementation-Defined Behavior (CWE-758) vulnerability in Bacnetstack Bacnet Stack. Its CVSS base score is 3.7 (Low).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 16th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

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…

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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.

CWE(s)
CWE-758

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
T1687 Exploitation for Defense Impairment Defense Impairment
Adversaries may exploit vulnerabilities in security software, infrastructure, or defensive components to degrade, disable, or otherwise continue to impair their ability to prevent, detect, or respond to malicious activity.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-21870Same product: Bacnetstack Bacnet Stack
CVE-2026-41475Same product: Bacnetstack Bacnet Stack
CVE-2026-26264Same product: Bacnetstack Bacnet Stack
CVE-2025-66624Same product: Bacnetstack Bacnet Stack
CVE-2026-41502Same product: Bacnetstack Bacnet Stack
CVE-2026-41503Same product: Bacnetstack Bacnet Stack
CVE-2026-21878Same product: Bacnetstack Bacnet Stack
CVE-2023-51773Same product: Bacnetstack Bacnet Stack
CVE-2023-30624Shared CWE-758
CVE-2026-34549Shared CWE-758

Affected Assets

bacnetstack
bacnet stack
≤ 1.4.3

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation can discover reliance on undefined behavior through cross-platform or stress testing.

SA-15 Development Process, Standards, and Tools partial match

Mandating a documented development process and coding standards directly discourages dependence on unspecified behavior.

SA-8 Security and Privacy Engineering Principles partial match

Engineering principles can require use of only well-defined language and API behaviors during development.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly prohibit use of undefined or implementation-defined behavior in code.

PR.PS-01 partial match
prevents

Consistent hardened configurations reduce the chance of relying on unspecified implementation details.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect some instances of undefined behavior but does not prevent the root weakness.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle requires defined, portable coding practices that reduce reliance on undefined behavior.

A.8.27 Secure system architecture and engineering principles partial match
degrades

Secure system architecture and engineering principles mandate use of well-specified interfaces and avoid undefined constructs.

A.8.28 Secure coding partial match
prevents

Secure coding explicitly prohibits constructs whose behavior is undefined, unspecified or implementation-defined.

References