Modicon M340 CVE-2024-5056 Patch BMXNOE0100/0110 & OT Network Mitigations

Schneider Electric has confirmed a security issue affecting the Modicon M340 family and two Ethernet communication modules — BMXNOE0100 and BMXNOE0110 — that can expose files or directories to external parties and, in some configurations, can prevent firmware updates or disrupt the embedded web/FTP services; Schneider has published an advisory and released firmware updates for the two Modbus/TCP modules while urging immediate network-level mitigations for other affected parts of the M340 product line.

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Background and overview​

The Modicon M340 is a widely deployed programmable automation controller (PAC) used across manufacturing, energy, and building automation. The two Ethernet communication modules at the center of this advisory — BMXNOE0100 (Modbus/TCP) and BMXNOE0110 (Modbus/TCP + FactoryCast/FTP) — provide standard network file and program transfer services to engineering workstations and supervisory systems. Those network-facing services are the attack surface for the reported vulnerability.
Schneider labeled the issue in their security notification SEVD-2024-163-01 and provided fixed firmware images for the two modules cited above: SV03.60 for BMXNOE0100 and SV06.80 for BMXNOE0110. Operators are instructed to verify integrity artifacts and reboot the module after applying the update. Schneider’s advisory and the firmware releases were published on Schneider Electric’s official security notification pages. (se.com)
At the same time, U.S. national authorities have cataloged related Modicon advisories that cover a range of issues across the M340 family and related modules. The broader advisory landscape includes several different CVE IDs and CWE classifications depending on the root cause observed; one record associated with file/directory exposure is tracked as CVE‑2024‑5056 (CWE‑552), which describes files or directories being accessible to external parties in a way that can affect firmware update functionality and webserver behavior. Independent vulnerability trackers and security databases have also indexed CVE‑2024‑5056. (avd.aquasec.com)

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Executive summary (technical highlights)​

• Affected devices: Modicon M340 processors (broadly reported), BMXNOE0100 and BMXNOE0110 communication modules. Schneider indicates “all versions” for some affected M340 components and has released module-specific fixes for the two Modbus/TCP modules.
• Vulnerability class: Files or Directories Accessible to External Parties (CWE‑552) — server-side file/directory access issues that can break firmware update workflows and degrade webserver behavior. CVE identifier: CVE‑2024‑5056 for the CWE‑552 instance.
• Attack vector: Network (remote); low attack complexity; no authentication required for the specific exposures described in the advisory records.
• Impact: Potential to prevent firmware updates and to disrupt web/FTP services or cause denial-of-service-like behavior when particular files or directories are removed or incorrectly exposed. Availability and integrity impacts are the principal concerns.
• Recommended immediate actions: Apply the published firmware (BMXNOE0100 SV03.60 and BMXNOE0110 SV06.80), verify integrity artifacts, reboot after patching, disable FTP when not needed, apply network segmentation and ACLs to block port 21/TCP from untrusted networks, and otherwise isolate ICS networks from business/internet-facing networks.

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What the vulnerability actually is — technical analysis​

Files and directory exposure (CWE‑552) explained​

The CWE‑552 class covers situations where a device’s filesystem, or files inside a web/FTP root, are accessible to external parties without sufficient access controls. In industrial devices that expose file services (HTTP, FTP, file upload/download APIs), the common failure modes are:

• Sensitive files placed under a publicly accessible root without per-file access controls.
• Directory traversal or directory enumeration that reveals or exposes configuration or firmware artifacts.
• Server logic that uses archive extraction or file operations without properly restricting paths or verifying caller privileges.

In the Modicon advisory tied to CVE‑2024‑5056, the measurable outcome Schneider and public trackers describe is twofold: 1) an attacker can cause a condition that prevents firmware updates from successfully applying, and 2) certain webserver behaviors can be disrupted when specific files or directories are removed or manipulated. Both outcomes are meaningful in OT: preventing firmware updates delays remediation and tampering with web/FTP resources can disable engineering workflows or produce inconsistent device states.

How an attacker would exploit the device​

Advisories describe network-accessible vectors that require no privileges and have low complexity. In practical terms, an attacker with network reachability to a device’s management interfaces (for example, via a compromised jump host, exposed VPN, or misconfigured firewall) could issue crafted FTP/HTTP requests or file operations that:

• Reveal or remove critical files used by the device’s update or webserver stack.
• Trigger the device to skip or fail integrity checks during firmware updates.
• Induce error conditions in the web/FTP server that lead to denial of service or inconsistent state.

Vendor and national advisories do not publish exploit code, and at disclosure time there were no widely confirmed active-exploitation reports specifically tied to this CVE; nevertheless, the combination of network access and low complexity raises the urgency for remediation. This “no known exploit in the wild” status is time‑sensitive and should be revalidated by operators before assuming safety.

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Affected inventory and firmware status — verified specifics​

Schneider’s official security notification SEVD‑2024‑163‑01 lists the Modicon M340 family and the two Ethernet modules as affected and supplies downloadable advisory documentation and integrity verification files alongside firmware builds. The firmware pages for the modules explicitly list:

• BMXNOE0100 — firmware SV03.60 (includes security fixes; integrity verification artifacts provided). (se.com)
• BMXNOE0110 — firmware SV06.80 (includes security fixes; integrity verification artifacts provided).

Other M340-related products and modules appear in broader Schneider / CISA advisories with overlapping or different CVEs (for example, other CVEs address memory management or information disclosure in other modules). Operators should not assume one firmware release addresses every M340-class advisory; instead, confirm the exact part number and SV (software version) on each module against Schneider’s advisory for that product. National advisories corroborate that some M340 processors are listed as “all versions” or are awaiting remediation plans — emphasizing the need to follow vendor guidance for each distinct part number. (cisa.gov)

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Immediate mitigations that reduce risk today​

Even before a firmware rollout is complete across all affected assets, a set of defensive measures materially reduces exposure:

• Patch the modules that have fixes — BMXNOE0100 SV03.60 and BMXNOE0110 SV06.80 — verify signature/integrity artifacts, reboot after update, and confirm operational status in a staging environment before broad deployment. (se.com)
• Disable FTP if unused. The advisory reiterates that FTP is commonly disabled by default; leave it disabled unless engineering processes require it. Where FTP is required, restrict which hosts can connect.
• Network segmentation — place PLCs and communication modules on dedicated OT networks separated by firewalls from corporate and internet-facing networks. Use strict ACLs to permit only known engineering hosts to reach device management ports.
• Block TCP/21 at the perimeter for OT subnets — disallow untrusted ingress to FTP services. If direct external access is unavoidable, use a hardened jump host and secure VPN with MFA; avoid exposing device ports directly to the internet.
• Harden engineering workstations — apply OS and application patches, run minimal services, and avoid using internet‑facing browsers on hosts that directly manage PLCs. Maintain offline backups of logic and program files to facilitate quicker recovery.
• Logging and detection — monitor for malformed FTP/HTTP sessions, repeated directory listings, or unexpected file deletions and add IDS/IPS rules covering abnormal FTP command sequences.

Operators should treat these mitigations as complementary: network controls buy time, but firmware fixes are the only long‑term remedy for the underlying code defects.

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Operational considerations and rollout guidance​

Applying firmware updates in industrial environments is operationally more complex than in IT. Key practical steps for secure rollout:

• Inventory (48 hours): Discover and catalog every Modicon M340 and related communication module on your network, including serial numbers and current SV (software version). Confirm whether each instance is reachable from untrusted networks.
• Isolate immediately: If any device is directly reachable from the internet, cut network exposure or place it behind a firewall with strict ACLs until patched.
• Test (7–14 days): Apply the module firmware updates in a lab or staging environment that mirrors production. Validate program integrity, communications, and failover/rollback procedures.
• Schedule (within 30 days where possible): Plan production maintenance windows to apply firmware; coordinate with operations teams to minimize downtime and confirm rollback plans. Keep a verified offline copy of PLC logic and configuration.
• Post‑update validation: After patching, confirm device behavior (network services, program integrity, project download/upload) and update asset records with the new SV.

A careful, staged approach preserves safety and availability while reducing cyber risk.

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Critical analysis — strengths, gaps, and remaining risk​

Where Schneider and the community did well​

• Timely module patches and integrity artifacts: Schneider released firmware images with integrity verification for the two specific Modbus/TCP modules, enabling operators to update and confirm the authenticity of downloads. This is essential for trust in OT firmware updates.
• Clear network mitigations: Advisories consistently recommend segmentation, blocking FTP from untrusted networks, and disabling unnecessary services — practical, effective steps that reduce immediate exposure. National authorities echoed these mitigations, which is useful for risk prioritization. (cisa.gov)

Where risk remains and why operators must not be complacent​

• Incomplete coverage for all M340 variants: Some M340 products are listed as “all versions” or are awaiting a remediation plan. That means many deployed controllers may not yet have a vendor-supplied firmware fix and will rely on network controls — an imperfect defense. Operators must track vendor follow-ups for each specific part number.
• Operational friction to patching: PLC firmware updates often require coordination, validation, and downtime — all practical constraints that delay patching and extend windows of exposure. Defense-in-depth is the practical imperative here.
• Potential for exploit tooling: While there were no widely reported in-the-wild exploit campaigns specific to CVE‑2024‑5056 at publication time, public disclosure of technical details makes the rapid development of proof-of-concept tools plausible. This elevates the urgency to patch exposed systems quickly. Treat “no known exploitation” as a temporary observation; re-check threat reports frequently.

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Windows‑centric checklist for engineering workstations and HMIs​

Many engineering workstations used to manage Modicon devices run Windows. The Windows engineering stack is a high‑value target; securing it reduces the probability of network pivoting into OT:

• Keep Windows and vendor automation suites updated and patched.
• Disable or uninstall unused Schneider utilities on operator machines (or keep them on isolated, hardened administrative workstations).
• Never use general web browsing on engineering workstations; separate general-purpose workstations from those that directly interface with PLCs.
• Enforce least privilege on accounts that manage PLCs; do not run engineering tools with elevated administrator accounts by default.
• Use jump hosts for remote access, and require MFA for VPN and remote management solutions.
• Maintain offline and tested backups of logic and project files for every PLC.

These steps reduce the attack surface from the Windows side and help ensure that patches applied to PLCs are not negated by compromised engineering hosts.

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Monitoring, reporting, and threat‑intelligence hygiene​

• Subscribe to Schneider Electric security notifications and download pages to receive integrity files and CVE mappings for relevant part numbers.
• Track national CERT/CISA ICS advisories for coordinated indicators of compromise and updates to severity scoring or observed exploitation. (cisa.gov)
• Add FTP and webserver anomaly detection to SOC/OT monitoring — malformed command patterns, repeated failed update attempts, and unexpected file-system changes should trigger investigation.
• Share suspected incidents through established internal channels and report confirmed or suspected exploitation to national authorities as directed by local policy.

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Final assessment and recommendations​

This vulnerability — classified as a files/directories exposure (CWE‑552) and recorded under CVE‑2024‑5056 in some vulnerability databases — underscores a familiar pattern in OT security: network‑accessible file services left without strict access controls create systemic risk. Schneider Electric has provided module-specific firmware updates (BMXNOE0100 SV03.60 and BMXNOE0110 SV06.80) and offers integrity verification artifacts; operators should prioritize those patches where applicable and follow vendor guidance for verification and rebooting. Equally important is a disciplined remediation program: asset inventory, segmentation, temporary service restrictions (disable FTP if unused), staged testing, and an update schedule that recognizes operational realities.
Cross-referencing the vendor advisory, national CERT guidance, and independent vulnerability trackers confirms the key facts in this article: the affected components, the nature of the vulnerability class, the available module fixes, and the standard mitigations recommended by industry authorities. Operators should assume that the threat landscape can change quickly; do not rely on a single mitigation. Implement both the immediate network-level controls and the firmware updates where available, and treat the remediation program as a coordinated OT/IT activity requiring testing, verification, and offline backups. (se.com)

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Quick action plan (concise checklist)​

• Inventory every Modicon M340 and related module and capture part numbers and SVs.
• Apply vendor firmware where available: BMXNOE0100 → SV03.60, BMXNOE0110 → SV06.80 (verify signatures). Reboot post-update.
• Block TCP/21 from untrusted networks and disable FTP if not required.
• Isolate PLC networks from the internet and corporate networks via segmentation and firewalls.
• Harden engineering workstations (Windows) and require jump hosts/MFA for remote access.
• Monitor for anomalous FTP/HTTP behavior and maintain incident reporting channels.

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Operators and asset owners should treat this advisory as actionable: patch the modules with available fixes immediately, enact network controls for all other affected product instances, and maintain vigilance for follow-up advisories from Schneider Electric and national authorities. The device‑side fixes for the BMXNOE modules are an important step, but the persistent risk profile for the broader M340 family reinforces the need for layered defenses and rapid, validated patch programs. (cisa.gov)
(Note: factual points such as CVE identifiers, CVSS vectors, and “no known exploitation” statuses were checked against Schneider Electric’s SEVD notification and multiple independent vulnerability trackers; these metadata elements are subject to change — operators must verify the latest vendor and national-advisory entries prior to decision-making.) (se.com)

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Source: CISA Schneider Electric Modicon M340, BMXNOE0100, and BMXNOE0110 | CISA