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VulnerabilityPublished

CVE-2026-40279: bacnet-stack · Reliance on Undefined, Unspecified, or Implementation-Defined Behavior

Affects bacnet-stackSource GCVE Database

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Not known to be exploited · CVSS 3.7 Low : upgrade to 1.4.3 when convenient.

Data as of 12 Nov 2026, 01:33 UTC

CVSS 3.1 base score
3.7Low
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (GitHub_M)CVSS 3.13.7
Patch
Available – fixed in 1.4.3
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 21 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 11 Nov 2026.

What to do

Upgrade bacnet-stack to 1.4.3.

Affected software

ProductAffectedFixed in
bacnet-stack bacnet-stackAffected
  • <1.4.3
Fixed in
  • 1.4.3

AI-suggested

Upgrade to bacnet-stack version 1.4.3 or later, where this vulnerability is fixed. No other mitigation is required as the issue is resolved in the official patch.

Description

CVE-2026-40279 is a vulnerability in the bacnet-stack open source BACnet protocol library for embedded systems. Versions prior to 1.4.3 contain a flaw in the decode_signed32() function, which reconstructs a 32-bit signed integer from four bytes using signed left shifts. When any byte has its highest bit set (≥ 0x80), this causes signed integer overflow, which is undefined behavior according to the C standard. This issue is fixed in version 1.4.3.

References

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