How severe is CVE-2026-21878?

CVE-2026-21878 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-21878 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21878?

CVE-2026-21878 primarily affects Bacnetstack Bacnet Stack. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-21878?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-21878 have an EU (EUVD) identifier?

Yes. CVE-2026-21878 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-6026.

When was CVE-2026-21878 published?

CVE-2026-21878 was published on 2026-02-13 and last updated on 2026-06-17.

CVE-2026-21878

CVE-2026-21878 is a high-severity vulnerability in Bacnetstack Bacnet Stack with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-22.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 0% (28th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-6026
Weakness: CWE-22
Affected product: Bacnetstack Bacnet Stack
Published: 2026-02-13
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-21878?: 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.
How severe is CVE-2026-21878?: CVE-2026-21878 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2026-21878 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21878?: CVE-2026-21878 primarily affects Bacnetstack Bacnet Stack. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-21878?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-21878 have an EU (EUVD) identifier?: Yes. CVE-2026-21878 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-6026.
When was CVE-2026-21878 published?: CVE-2026-21878 was published on 2026-02-13 and last updated on 2026-06-17.

References

Affected products (2)

cpe:2.3:a:bacnetstack:bacnet_stack:1.5.0:rc1:*:*:*:*:*:*
cpe:2.3:a:bacnetstack:bacnet_stack:1.5.0:rc2:*:*:*:*:*:*

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