CVE
BACnet Stack heap out-of-bounds read in RAMFS file handling
Affects bacnet-stack using the RAMFS-backed FILE object backend with a writable FILE object. Fixed in bacnet-stack 1.5.1.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- Exploited
- No known exploitation
- Fix
- Fixed in 1.5.1
- Who is exposed
- Specific setups only
Do first: Check whether your setup matches what the bug needs. Uses the RAMFS-backed FILE object backend. Target FILE object is writable.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- FIRST's estimate of the chance attackers exploit it in the next 30 days, updated daily.What do these mean? →
- 0.29% · 22nd percentile
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 21/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
BACnet Stack, a BACnet open source protocol stack C library for embedded systems, contains a heap out-of-bounds read in its RAMFS-backed FILE object handling. A remote attacker can trigger it without logging in by sending two consecutive AtomicWriteFile record-access append requests, and the flaw can impact system availability.
Original description
BACnet Stack is a BACnet open source protocol stack C library for embedded systems. Prior to version 1.5.1, the RAMFS-backed FILE object implementation stores appended records as NUL-terminated strings, but its record-counting logic later walks the buffer as if an additional terminating empty record were present. As a result, two consecutive AtomicWriteFile(record-access) append requests can cause record_count() to call bacnet_strnlen() on a pointer that is already one byte past the end of the heap allocation. This issue has been patched in versions 1.5.1 and 1.6.0.
Who should check
Teams running bacnet-stack 1.5.0 with the RAMFS-backed FILE object backend and writable FILE objects, such as embedded BACnet devices.
“In bacnet-stack 1.5.0 ( master branch commit 932e347 ), the RAMFS-backed FILE object implementation”
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure12/25Specific setups only, reachable over the network without a login
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.7/10CVSS 8.7
- No patch0/5No signal
What would change the score
- Would score about 71 if added to CISA KEV
- Would score about 66 if CISA's SSVC rates exploitation active
What to do
Check whether your setup matches what the bug needs.
Uses the RAMFS-backed FILE object backend. Target FILE object is writable.Upgrade to a fixed version: 1.5.1.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-62976 (BACnet Stack: Consecutive AtomicWriteFile(record-access) appends can trigger a heap out-of-bounds read in the RAMFS file backend), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-62976 (entry last updated 2026-11-13):
Affected:
- bacnet-stack bacnet-stack: fixed in 1.5.1
Fixed versions: 1.5.1.
Conditions (all must be true for the bug to be hit):
- Uses the RAMFS-backed FILE object backend. (source: https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-32jj-x86x-w98w)
- Target FILE object is writable. (source: https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-32jj-x86x-w98w)
Setup: the bug needs a feature or setting that is off by default or uncommon. Check whether each asset has it on.
Attacker needs: network access, no login, no user action.
CISA KEV: CVE-2026-62976 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-62976 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-32jj-x86x-w98w
- https://github.com/bacnet-stack/bacnet-stack/pull/1408
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.
Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.
Entry: https://cve.now/CVE-2026-62976
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-62976"}.Timeline
- CVE published
- First seen by cve.now
Affected versions
- bacnet-stack bacnet-stack
fixed in 1.5.1
Evidence 4
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 1
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-62976
Is CVE-2026-62976 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
Appending two records to the same writable FILE object can read past the end of a heap buffer, because the RAMFS-backed FILE object stores appended records as NUL-terminated strings. This can cause a crash, denial of service, or other undefined behavior.Source: github.com
Which versions are affected by CVE-2026-62976?
bacnet-stack: before 1.5.1.Source: cve.now feed data
Am I affected, and how do I check?
The issue affects bacnet-stack builds that use the RAMFS-backed FILE object implementation and write to a FILE object, before the fix in 1.5.1. To check, confirm the bacnet-stack version in use and whether its FILE object uses the RAMFS-backed backend.Source: github.com
How do I fix CVE-2026-62976?
Upgrade bacnet-stack to 1.5.1, which is the listed fixed version for this vulnerability.Source: github.com