CVE-2026-40279
low-risk
Published 2026-04-21
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.
Do I need to act?
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0.04% chance of exploitation
EPSS score — low exploit probability
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Not on CISA KEV list
No confirmed active exploitation reported to CISA
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Patch status unknown
Check vendor advisories for fix availability and mitigation guidance
3
CVSS 3.7/10
Low
NETWORK
/ HIGH complexity
Affected Products (1)
Bacnet Stack
Affected Vendors
18
/ 100
low-risk
Severity
13/34 · Low
Exploitability
0/34 · Minimal
Exposure
5/34 · Minimal