PatchTheCVECVE-2026-40279: BACnet Stack is a BACnet open source protocol stack C library for embedded systems
CVE-2026-40279 is a low-severity flaw (CVSS 3.7) affecting bacnet stack. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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 UndefinedBehaviorS
Why this priority
- Public exploit reference
- Remotely exploitable, no login, no user action
A fixed release or distro patch exists.
Risk facts
| CVSS score | 3.7 (Low) |
| Attack vector | Network (remote) |
| Attack complexity | High |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 0.2% (top 85%) |
| CISA exploited list | No |
| Weakness | CWE-758 |
| Published | 2026-04-21 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-40279?
bacnet stack: upgrade to 1.4.3. Exact commands for each OS are on this page.
Is CVE-2026-40279 being exploited?
CVE-2026-40279 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2026-40279 affect?
CVE-2026-40279 affects bacnet stack. Severity is low (CVSS 3.7). 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
How urgent is CVE-2026-40279?
Priority 27/100. Public exploit reference; Remotely exploitable, no login, no user action
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