# CVE-2026-62975: BACnet Stack: Replacing a RAMFS record with a shorter one via `AtomicWriteFile(record-access)` can trigger a heap out-of-bounds read

Status: published. Published: 2026-11-13. Updated: 2026-11-13.

BACnet Stack is a BACnet open source protocol stack C library for embedded systems. Prior to version 1.5.1, the RAMFS-backed FILE implementation accepts AtomicWriteFile(record-access) requests that replace existing records with caller-controlled content. If a client replaces a record with shorter data, the backend can shrink the heap allocation and then continue processing with a trailing-copy length derived from the old layout. During that replace path, the RAMFS backend computes the trailing-copy length from the old file layout, then shrinks the heap allocation, and finally uses the stale length in memmove(). As a result, the source range of that memmove() can extend beyond the end of the reallocated heap buffer, producing a heap out-of-bounds read. This issue has been patched in versions 1.5.1 and 1.6.0.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- bacnet-stack / bacnet-stack: < 1.5.1 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 4.0: 6.9 (medium); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-125

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-cf8g-hp9m-9fvv (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/bacnet-stack/bacnet-stack/pull/1408 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-62975; retrieved 2026-11-13; source updated 2026-11-13

Revision: f1fcd94216463dfe8c037c311d1abbf61becfc22ed62fa23002d3fb5c26af36c

Canonical: https://y2.dev/cve/CVE-2026-62975

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