{"id":"CVE-2026-40279","summary":"BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`","details":"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.","aliases":["GHSA-326g-j95f-gmxv"],"modified":"2026-07-08T08:05:09.609187429Z","published":"2026-04-21T16:29:16.125Z","database_specific":{"cwe_ids":["CWE-758"],"cna_assigner":"GitHub_M","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40279.json"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40279.json"},{"type":"ADVISORY","url":"https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-40279"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/bacnet-stack/bacnet-stack","events":[{"introduced":"0"},{"fixed":"6d2d251ca4f4d932664add702b236279863d630a"}],"database_specific":{"extracted_events":[{"introduced":"0"},{"fixed":"1.4.3"}],"source":["AFFECTED_FIELD","CPE_RANGE"],"cpe":"cpe:2.3:a:bacnetstack:bacnet_stack:*:*:*:*:*:*:*:*"}}],"versions":["bacnet-stack-1.4.0","bacnet-stack-1.3.8","bacnet-stack-1.3.7","bacnet-stack-1.3.6","bacnet-stack-1.3.5","bacnet-stack-1.3.4","bacnet-stack-1.3.3","bacnet-stack-1.3.2","bacnet-stack-1.3.1","bacnet-stack-1.3.0","bacnet-stack-1.2.0","bacnet-stack-1.1.1","bacnet-stack-1.0.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-40279.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L"}]}