Is CVE-2026-21878 actively exploited?

A proof-of-concept exploit is publicly available for CVE-2026-21878, but active exploitation has not been confirmed.

Can CVE-2026-21878 be exploited remotely?

Yes. CVE-2026-21878 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2026-21878?

CVE-2026-21878 has a CVSS score of 7.5 (HIGH) and an EPSS exploitation probability of 0.05%.

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HIGHPOC

CVE-2026-21878

CWE-22Published: February 13, 2026· Updated: Feb 18, 2026

7.5

CVSS v3.1

EPSS:0.05%probability of exploitation in 30 daysPercentile:15.6th

Official 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.

NVD Source

Technical Analysis

CVE-2026-21878 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in full integrity compromise (data manipulation), with a CVSS base score of 7.5.

A proof-of-concept (PoC) exploit exists for CVE-2026-21878. While not yet confirmed in active campaigns, the availability of PoC code increases exploitation risk substantially.