How severe is CVE-2026-40279?

CVE-2026-40279 has a CVSS 3.x base score of 3.7, rated low severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.

Is CVE-2026-40279 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (15th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-40279?

CVE-2026-40279 affects Bacnetstack Bacnet Stack. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-40279?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-40279 have an EU (EUVD) identifier?

Yes. CVE-2026-40279 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-24166.

When was CVE-2026-40279 published?

CVE-2026-40279 was published on 2026-04-21 and last updated on 2026-06-17.

CVE-2026-40279

CVE-2026-40279 is a low-severity vulnerability in Bacnetstack Bacnet Stack with a CVSS 3.x base score of 3.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-758.

Key facts

Severity: Low (CVSS 3.x base score 3.7)
EPSS exploit prediction: 0% (15th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-24166
Weakness: CWE-758
Affected product: Bacnetstack Bacnet Stack
Published: 2026-04-21
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2026-40279?: 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.
How severe is CVE-2026-40279?: CVE-2026-40279 has a CVSS 3.x base score of 3.7, rated low severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
Is CVE-2026-40279 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (15th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-40279?: CVE-2026-40279 affects Bacnetstack Bacnet Stack. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-40279?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-40279 have an EU (EUVD) identifier?: Yes. CVE-2026-40279 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-24166.
When was CVE-2026-40279 published?: CVE-2026-40279 was published on 2026-04-21 and last updated on 2026-06-17.

References

https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-326g-j95f-gmxv

Affected products (1)

cpe:2.3:a:bacnetstack:bacnet_stack:*:*:*:*:*:*:*:*

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