Is CVE-2026-21870 actively exploited?

A proof-of-concept exploit is publicly available for CVE-2026-21870, but active exploitation has not been confirmed.

Can CVE-2026-21870 be exploited remotely?

No. CVE-2026-21870 requires local access to exploit.

What is the CVSS score of CVE-2026-21870?

CVE-2026-21870 has a CVSS score of 5.5 (MEDIUM) and an EPSS exploitation probability of 0.01%.

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MEDIUMPOC

CVE-2026-21870

CWE-193Published: February 13, 2026· Updated: Feb 18, 2026

5.5

CVSS v3.1

EPSS:0.01%probability of exploitation in 30 daysPercentile:1.6th

Official 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.

NVD Source

Technical Analysis

CVE-2026-21870 requires local access, meaning attackers must already have a foothold on the target system.

Exploitation does not require any privileges, though user interaction (Required) is needed, which slightly reduces the risk of mass automated attacks.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 5.5.

A proof-of-concept (PoC) exploit exists for CVE-2026-21870. While not yet confirmed in active campaigns, the availability of PoC code increases exploitation risk substantially.