CVE-2026-40279Public exploitNetwork attack vector

Availability degradation via signed left shifts

Published Apr 21, 2026 · Updated Apr 21, 2026

Undefined behavior in BACnet Stack before 1.4.3 allows remote attackers to trigger invalid signed shifts via crafted APDU bytes. The decode_signed32() function in src/bacnet/bacint.c casts each APDU byte to int32_t before left-shifting it, so a high-bit byte produces an unrepresentable signed result. The effect requires a compiler build that turns this undefined behavior into incorrect code; no production miscompilation or direct exploit primitive is known.

CVSS severity3.7
Low
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Undefined behavior in BACnet Stack before 1.4.3 allows remote attackers to trigger invalid signed shifts via crafted APDU bytes. The decode_signed32() function in src/bacnet/bacint.c casts each APDU byte to int32_t before left-shifting it, so a high-bit byte produces an unrepresentable signed result. The effect requires a compiler build that turns this undefined behavior into incorrect code; no production miscompilation or direct exploit primitive is known.

The record

CVE
CVE-2026-40279
Published
Apr 21, 2026
Updated
Apr 21, 2026
Vendor
BACnet Stack
Product
BACnet Stack
Classifications
CWE-758
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 21, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 21, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.4.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

BACnet Stack · BACnet Stackversion=< 1.4.3

Published CVSS scores

3.7GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-758Reliance on Undefined, Unspecified, or Implementation-Defined Behavior

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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