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TI-2026-21234 Aliases CVE-2026-26264

BACnet Stack WriteProperty decoding length underflow leads to OOB read and crash

Priority HIGH 73CWE-125Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
—
Confidentiality · integrity · availability
High · None · High
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA.

Summary

BACnet Stack is a BACnet open source protocol stack C library for embedded systems. Prior to 1.5.0rc4 and 1.4.3rc2, a malformed WriteProperty request can trigger a length underflow in the BACnet stack, leading to an out‑of‑bounds read and a crash (DoS). The issue is in wp.c within wp_decode_service_request. When decoding the optional priority context tag, the code passes apdu_len - apdu_size to bacnet_unsigned_context_decode without validating that apdu_size <= apdu_len. If a truncated APDU reaches this path, apdu_len - apdu_size underflows, resulting in a large size being used for decoding and an out‑of‑bounds read. This vulnerability is fixed in 1.5.0rc4 and 1.4.3rc2.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00427 37th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed bacnet-stack (bacnet-stack): 1.5.0rc4, 1.4.3rc2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
bacnet-stackbacnet-stack1.5.0rc1 to before 1.5.0rc4; before 1.4.3rc21.5.0rc4, 1.4.3rc2Patch availableCNA
  • bacnet-stack Vendorbacnet-stack Affected 1.5.0rc1 to before 1.5.0rc4; before 1.4.3rc2 Fixed in 1.5.0rc4, 1.4.3rc2 Patch available CNA

CPE configurations NVD · 5

CPEVersionsRoleVendor
cpe:2.3:a:bacnetstack:bacnet_stack:*:*:*:*:*:*:*:*1.4.0 to before 1.4.3Vulnerablebacnet-stack
cpe:2.3:a:bacnetstack:bacnet_stack:1.4.3:rc1:*:*:*:*:*:*1.4.3 rc1Vulnerablebacnet-stack
cpe:2.3:a:bacnetstack:bacnet_stack:1.5.0:rc1:*:*:*:*:*:*1.5.0 rc1Vulnerablebacnet-stack
cpe:2.3:a:bacnetstack:bacnet_stack:1.5.0:rc2:*:*:*:*:*:*1.5.0 rc2Vulnerablebacnet-stack
cpe:2.3:a:bacnetstack:bacnet_stack:1.5.0:rc3:*:*:*:*:*:*1.5.0 rc3Vulnerablebacnet-stack
  • cpe:2.3:a:bacnetstack:bacnet_stack:*:*:*:*:*:*:*:* Versions 1.4.0 to before 1.4.3 Vulnerable ·bacnet-stack
  • cpe:2.3:a:bacnetstack:bacnet_stack:1.4.3:rc1:*:*:*:*:*:* Versions 1.4.3 rc1 Vulnerable ·bacnet-stack
  • cpe:2.3:a:bacnetstack:bacnet_stack:1.5.0:rc1:*:*:*:*:*:* Versions 1.5.0 rc1 Vulnerable ·bacnet-stack
  • cpe:2.3:a:bacnetstack:bacnet_stack:1.5.0:rc2:*:*:*:*:*:* Versions 1.5.0 rc2 Vulnerable ·bacnet-stack
  • cpe:2.3:a:bacnetstack:bacnet_stack:1.5.0:rc3:*:*:*:*:*:* Versions 1.5.0 rc3 Vulnerable ·bacnet-stack

Remediation

  • Fix · CNA bacnet-stack (bacnet-stack) Fixed in 1.5.0rc4, 1.4.3rc2

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-26264

References

Exploit 1

Patch 1

  • TI-2026-30089 BACnet Stack: Out-of-Bounds Read in ReadPropertyMultiple Property Decoder via Deprecated Tag Parser CVSS 4.0HIGH 8.7
  • TI-2026-30088 BACnet Stack: Off-by-One Out-of-Bounds Read in ReadPropertyMultiple Object ID Decoder CVSS 4.0HIGH 8.7
  • TI-2026-30063 BACnet Stack: Out-of-Bounds Read in WritePropertyMultiple Decoder via Deprecated Tag Parser CVSS 4.0HIGH 8.7
  • TI-2026-17579 BACnet Stack Improperly Limits Pathnames to a Restricted Directory CVSS 3.1HIGH 7.5
  • TI-2025-41018 BACnet-stack MS/TP reply matcher OOB read CVSS 3.1HIGH 7.5
  • TI-2026-29061 BACnet Stack: Undefined-behavior signed left shift in `decode_signed32()` CVSS 3.1LOW 3.7
See all 8 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences