Vulnerability in Bacnet-Stack
CVE-2026-40279
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L.
EPSS exploit prediction
EPSS: 0.003 (24.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 25th percentile — 24.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001
Affected products
- Bacnet-Stack — versions < 1.4.3
- Bacnetstack Bacnet Stack
Weakness classification (CWE)
References
- github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv (Exploit, Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-40279?
- CVE-2026-40279 is a low-severity vulnerability in Bacnet-Stack, classified under CWE-758. CVSS score: 3.7/10. Published 2026-04-21.
- How severe is CVE-2026-40279?
- Low severity. CVSS v3 base score is 3.7 out of 10.