CVE-2026-21878: BACnet Stack Improperly Limits Pathnames to a Restricted Directory

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-02-13 · updated 2026-06-17
Weakness: CWE-22

Description

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.

Affected products

bacnet-stack: 1.5.0-rc1, 1.5.0-rc2

References

https://github.com/bacnet-stack/bacnet-stack/commit/c5dc00a77b4bc2550befa67a930b333e299c18f3
https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-p8rx-c26w-545j

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