How serious is CVE-2026-21870?

This vulnerability has a CVSS score of 5.5 out of 10, classified as MEDIUM severity. Proof-of-concept exploit code is publicly available, making this an active threat.

Is there exploit code available for CVE-2026-21870?

Yes, proof-of-concept exploit code for CVE-2026-21870 is publicly available on GitHub and security research platforms. This increases the risk of active exploitation.

Which products are affected by CVE-2026-21870?

CVE-2026-21870 affects bacnetstack bacnet stack. Check the full CVE details for specific version information.

How do I fix CVE-2026-21870?

To remediate CVE-2026-21870, check for security patches from bacnetstack. Apply all available updates and security patches. If no patch is available, implement recommended workarounds or security controls to mitigate the risk.

CVE-2026-21870

Medium

|5.5

Exploit Available

Plain English Summary

AI-powered analysis for quick understanding

This vulnerability allows an attacker to crash the BACnet application by sending a specially crafted string that exceeds the buffer limit, leading to a stack overflow. The attacker needs to exploit the ubasic interpreter in specific versions of the BACnet Protocol Stack library, which improperly handles long strings, causing the application to terminate unexpectedly.

Technical 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 Vector Analysis

Attack VectorLocal

Attack ComplexityLow

Privileges RequiredNone

User InteractionRequired

Confidentiality ImpactNone

Integrity ImpactNone

Availability ImpactHigh

ScopeUnchanged

Vector String

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Exploit Resources

Search for proof-of-concept code and exploit modules

GitHub Search Exploit-DB Nuclei Templates Metasploit Vulners

Official References

NIST NVD

Est. Bounty

$759($500-$1K)

Vendor Response

Grade APatched in 5 days

Quick Information

Published

Feb 13, 2026

7 days ago

Last Modified

Feb 18, 2026

2 days ago

Vendor

bacnetstack

Product

bacnet stack