Read the docs
TI-2026-17579 Aliases CVE-2026-21878

BACnet Stack Improperly Limits Pathnames to a Restricted Directory

Priority HIGH 72CWE-22Published · Updated

Key facts

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

Attack profile from CVSS 3.1 · CNA. Fix status from CNA.

Summary

BACnet Stack is a BACnet open source protocol stack C library for embedded systems. Prior to 1.5.0.rc3, a vulnerability has been discovered in BACnet Stack's file writing functionality where there is no validation of user-provided file paths, allowing attackers to write files to arbitrary directories. This affects apps/readfile/main.c and ports/posix/bacfile-posix.c. This vulnerability is fixed in 1.5.0.rc3.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00413 35th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed bacnet-stack (bacnet-stack): 1.5.0.rc3

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-stackbefore 1.5.0.rc31.5.0.rc3Patch availableCNA
  • bacnet-stack Vendorbacnet-stack Affected before 1.5.0.rc3 Fixed in 1.5.0.rc3 Patch available CNA

CPE configurations NVD · 2

CPEVersionsRoleVendor
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: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

Remediation

  • Fix · CNA bacnet-stack (bacnet-stack) Fixed in 1.5.0.rc3

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-21878

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-2026-21234 BACnet Stack WriteProperty decoding length underflow leads to OOB read and crash CVSS 4.0HIGH 7.8
  • 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