Reliance on Undefined, Unspecified, or Implementation-Defined Behavior Affecting bacnet package, versions [,1.4.3)
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-UNMANAGED-BACNET-16152886
- published23 Apr 2026
- disclosed22 Apr 2026
- creditJorge Barredo
Introduced: 22 Apr 2026
NewCVE-2026-40279 (opens in a new tab)How to fix?
Upgrade bacnet to version 1.4.3 or higher.
Overview
Affected versions of this package are vulnerable to Reliance on Undefined, Unspecified, or Implementation-Defined Behavior via the decode_signed32() function in src/bacnet/bacint.c that 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.
PoC
/* poc_bacnet001.c */
#include
#include "bacnet/bacint.h"
int main(void) {
uint8_t apdu[4] = { 0x91, 0x02, 0x00, 0x00 }; /* 0x91 = 145, bit 7 set */
int32_t v;
decode_signed32(apdu, &v);
return 0;
}