CVE
BACnet Stack out-of-bounds read and write in atomic file requests
Only affects bacnet-stack 1.4.2 through 1.5.0 builds that use the RAM file backend (bramfs/bsramfs). Fixed in 1.4.5 and 1.5.1.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
- Exploited
- Proof of concept public, per CISA
- Fix
- Fixed in 1.4.5, 1.5.1
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 1.4.5, 1.5.1.
- 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? →
- 0.33% · 26th 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? →
- 44/100 · 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? →
- Unclear
- 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
- Exploitation: poc
- Automatable: yes
- Technical impact: partial
Summary
The bacnet-stack library has a flaw in how it checks the starting position of file read and write requests (AtomicReadFile and AtomicWriteFile) before passing them to its RAM file handling. A remote attacker who can reach the service can send such requests without logging in and cause the process to crash, read adjacent memory, or write past a buffer and corrupt heap memory.
Original description
BACnet Stack is a BACnet open source protocol stack C library for embedded systems. From versions 1.4.2 to before 1.4.5, and 1.5.0 to before 1.5.1, a signed fileStartPosition taken from AtomicReadFile and AtomicWriteFile stream-access requests is not validated tightly enough before it reaches the RAM file backends. Practical impact includes: reliable denial of service via process crash, out-of-bounds read that may expose adjacent memory contents, or out-of-bounds write that may corrupt heap memory and destabilize the process. This issue has been patched in versions 1.4.5 and 1.5.1.
Who should check
Teams running bacnet-stack 1.4.2 through 1.5.0 with the RAM file backend (bramfs or bsramfs) on BACnet/IP devices that accept AtomicReadFile or AtomicWriteFile requests.
“>= 1.4.2, <= 1.5.0”
cve.now Index
- Exploitation15/40CISA rates a proof of concept as public
- Exposure20/25No login or user action needed, CISA rates it automatable · Unknown: Advisories don't say whether default setups are affected
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.6/10CVSS 8.6
- No patch0/5No signal
What would change the score
- Would score about 74 if added to CISA KEV
- Would score about 69 if CISA's SSVC rates exploitation active
- Would score about 49 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 1.4.5, 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-2026-49990 (BACnet Stack: AtomicReadFile/AtomicWriteFile stream fileStartPosition validation flaw causes out-of-bounds read/write in RAM file backends), 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-2026-49990 (entry last updated 2026-11-13):
Affected:
- bacnet-stack bacnet-stack: from 1.4.2, fixed in 1.4.5; from 1.5.0, fixed in 1.5.1
Fixed versions: 1.4.5, 1.5.1.
Conditions (all must be true for the bug to be hit):
- Affects bacnet-stack versions 1.4.2 up to 1.5.0 (patched in 1.4.5 and 1.5.1). (source: https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-8759-hx7g-94qx)
- Only applies when the target build uses the vulnerable RAM file backend path (bramfs/bsramfs). (source: https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-8759-hx7g-94qx)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, no login, no user action.
CISA KEV: CVE-2026-49990 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-49990 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-8759-hx7g-94qx
- https://github.com/bacnet-stack/bacnet-stack/pull/1362
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-2026-49990
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-2026-49990"}.Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: poc · Automatable: yes · Technical impact: partial
- Record last updated
Affected versions
- bacnet-stack bacnet-stack
From 1.4.2 · fixed in 1.4.5; From 1.5.0 · 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-2026-49990
Is CVE-2026-49990 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. CISA's SSVC assessment notes a proof of concept exists. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
AtomicReadFile and AtomicWriteFile do not properly validate the fileStartPosition value for stream access, so reads or writes can go outside the bounds of the RAM file backend. The vendor's stated impact is a process crash, an out-of-bounds read that may expose adjacent memory, or an out-of-bounds write that may corrupt heap memory.Source: github.com
Which versions are affected by CVE-2026-49990?
bacnet-stack: from 1.4.2 before 1.4.5; from 1.5.0 before 1.5.1.Source: cve.now feed data
Am I affected, and how do I check?
Versions 1.4.2 up to 1.5.0 are affected, and only when the build uses the vulnerable RAM file backend path (bramfs/bsramfs). To check, look at the bacnet-stack version in use and whether the build includes the bramfs or bsramfs file backend.Source: github.com
How do I fix CVE-2026-49990?
Upgrade to bacnet-stack 1.4.5 on the 1.4.x line or to 1.5.1 on the 1.5.x line.Source: github.com