CVE-2026-40279 json
BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()`
published 2026-04-21 6 mo ago modified 2026-06-17 4 mo ago also EUVD-2026-24166
- cvss
- 3.7
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.2%
- EPSS 0.2% chance of exploitation in 30 days, percentile 15%
- public exploits
- 0
- none known
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.
Patch / fix
- bacnetstack bacnet_stack 1.4.3
CISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- no
- Technical impact
- partial
- Assessed
- 6 mo ago
Exploit prediction
0.24% chance of exploitation in the next 30 days, higher than 15% of all scored CVEs (FIRST EPSS, 2026-11-08).
Exploits and checks
- github.com https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 3.7 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L |
Affected products
- bacnet-stack bacnet-stack
Classification
- Weakness
-
- CWE-758 Reliance on Undefined, Unspecified, or Implementation-Defined Behavior
References
-
github.com
/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv
exploit, mitigation, vendor-advisory
Sources
- CVE List CVE-2026-40279
- NVD CVE-2026-40279
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.