Low severity · published Apr 21, 2026
CVE-2026-40279
BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`
3.7
CVSS
0.2%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 15% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
BA
bacnet-stack · bacnet-stack
< 1.4.3 · source: vendor
BS
Bacnet Stack · Bacnetstack
before 1.4.3 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-40279
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-40279
Exploit
https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv
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