BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`

{
  "id": "480d62e97315ce166fc4313e6a305d470c7c154bc735e0642183d665d66bd512",
  "url": "https://osv.dev/vulnerability/CVE-2026-40279",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`",
    "summary": "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.",
    "evidence": "osv:CVE-2026-40279",
    "products": [],
    "severity": "low",
    "structured": {
      "id": "CVE-2026-40279",
      "aliases": [
        "CVE-2026-40279",
        "GHSA-326g-j95f-gmxv"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/bacnet-stack/bacnet-stack",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "6d2d251ca4f4d932664add702b236279863d630a"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "1.4.3"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "cpe": "cpe:2.3:a:bacnetstack:bacnet_stack:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "1.4.3"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "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"
          }
        }
      ],
      "modified": "2026-10-28T02:30:37.632468571Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40279.json",
        "https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-40279"
      ],
      "provider_metadata": {
        "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"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-40279",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 504769,
  "published_at": "2026-04-21T16:29:16.125+00:00"
}