Vulnerability Description
BACnet Protocol Stack library provides a BACnet application layer, network layer and media access (MAC) layer communications services. In 1.4.2, 1.5.0.rc2, and earlier, an off-by-one stack-based buffer overflow in the ubasic interpreter causes a crash (SIGABRT) when processing string literals longer than the buffer limit. The tokenizer_string function in src/bacnet/basic/program/ubasic/tokenizer.c incorrectly handles null termination for maximum-length strings. It writes a null byte to dest[40] when the buffer size is only 40 (indices 0-39), triggering a stack overflow.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Bacnetstack | Bacnet Stack | <= 1.4.2 |
Related Weaknesses (CWE)
References
- https://github.com/bacnet-stack/bacnet-stack/commit/4e1176394a5ae50d2fd0b5790d9bPatch
- https://github.com/bacnet-stack/bacnet-stack/pull/1196Patch
- https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-pc83-wp6w-Vendor AdvisoryExploit
FAQ
What is CVE-2026-21870?
CVE-2026-21870 is a vulnerability with a CVSS score of 5.5 (MEDIUM). BACnet Protocol Stack library provides a BACnet application layer, network layer and media access (MAC) layer communications services. In 1.4.2, 1.5.0.rc2, and earlier, an off-by-one stack-based buffe...
How severe is CVE-2026-21870?
CVE-2026-21870 has been rated MEDIUM with a CVSS base score of 5.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-21870?
Check the references section above for vendor advisories and patch information. Affected products include: Bacnetstack Bacnet Stack.