Unauthenticated arbitrary file write via path traversal
Published Feb 13, 2026 · Updated Feb 13, 2026
Path traversal in BACnet Stack before 1.5.0.rc3 allows remote attackers to write files outside intended directories over BACnet. The POSIX AtomicWriteFile handler passes a network-supplied pathname directly to fopen, while the readfile client opens its unvalidated destination argument. No authentication or user interaction is required for the network service path; successful writes remain limited by the process account's filesystem permissions.
Summary
What happened
Path traversal in BACnet Stack before 1.5.0.rc3 allows remote attackers to write files outside intended directories over BACnet. The POSIX AtomicWriteFile handler passes a network-supplied pathname directly to fopen, while the readfile client opens its unvalidated destination argument. No authentication or user interaction is required for the network service path; successful writes remain limited by the process account's filesystem permissions.
The record
- CVE
- CVE-2026-21878
- Published
- Feb 13, 2026
- Updated
- Feb 13, 2026
- Vendor
- BACnet Stack
- Product
- BACnet Stack
- Classifications
- CWE-22, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Feb 13, 2026CVE publishedPublication date reported by the CVE source.
- Feb 13, 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.
- Affected versionversion=< 1.5.0.rc3
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
- GHSA-p8rx-c26w-545j reproduction methodproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
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