Rockwell Automation’s CompactLogix 5370 line has been flagged in a coordinated advisory as vulnerable to a denial-of-service condition when sent a malformed Common Industrial Protocol (CIP) forward open message, an issue tracked as
CVE‑2025‑11743 and rated with a CVSS v3.1 base score of
6.5. The flaw can force a
major nonrecoverable fault on affected controllers that requires a manual restart to recover, and Rockwell has published fixed firmware versions alongside guidance for mitigation and defense‑in‑depth controls.
Background
Industrial control systems (ICS) and programmable logic controllers (PLCs) like the Rockwell Automation
CompactLogix 5370 series sit at the heart of modern manufacturing and critical infrastructure. These devices use CIP (Common Industrial Protocol) over EtherNet/IP to manage sessions, read/write data, and establish control connections. The vulnerability in question stems from
improper validation of a specified quantity in input — effectively a malformed CIP forward open message that the controller does not safely handle, producing a catastrophic fault condition. The impact is availability focused: a DoS that halts the device until it is restarted.
Rockwell’s advisory and the federal summary used in coordination list the affected firmware ranges as known vulnerable and identify the fixed releases operators should migrate to. For environments that cannot immediately upgrade, the vendor and national guidance recommend layered compensations — network segmentation, limited adjacency exposure, and secure remote access practices.
What’s the technical problem? — A concise technical summary
- Vulnerability class: Improper Validation of Specified Quantity in Input (mapped to CWE family).
- Trigger: A malformed CIP forward open message sent to a CompactLogix 5370 device.
- Failure mode: The controller experiences a major nonrecoverable fault (MNRF) or similarly critical fault state.
- Recovery requirement: A manual restart or equivalent physical intervention is required to return the device to normal operation.
- Attack vector and scope: The CVSS vector indicates the attack is adjacent-network (AV:A), meaning an attacker must be on the same local network segment or able to send adjacent network traffic; it is not described as directly exploitable from the open Internet.
This is not a stealth privilege‑escalation or remote code execution bug; its primary impact is availability — which, in ICS terms, frequently maps directly to production losses, safety system interruptions, and operational risk.
Affected products and remediation status
Affected firmware lines
Rockwell identifies CompactLogix 5370 firmware lines in multiple version bands as affected up to published cutoff points. The vendor lists the following vulnerable versions:
- CompactLogix 5370: versions at or below certain release numbers (vendors typically publish exact version cutoffs; confirm installed revision strings on devices before applying updates).
Fixed releases
Rockwell reports fixed releases in the following firmware versions and release trains — customers should upgrade to these or later to remediate the vulnerability:
- Version 37.011 and later
- Version 34.016
- Version 35.015
- Version 36.012
Operators are strongly advised to move to one of the fixed versions appropriate for their SKU and to follow the vendor’s published update instructions and compatibility notes. If a device cannot be upgraded, Rockwell’s advisory and national guidance present compensating controls as temporary risk reduction measures.
The operational impact — realistic scenarios
Industrial networks are not isolated silos; disruption to a PLC can cascade into supervisory systems, engineering workstations, and HMI displays. Consider these practical scenarios:
- A maintenance engineer uses remote access through a jump host; an attacker or malformed tool from the connected subnet sends a crafted CIP forward open to the CompactLogix 5370 controller, producing an MNRF and forcing an unplanned production stop.
- A targeted adversary with local network access repeatedly triggers the fault on a set of controllers during peak shift change, causing repeated stoppages, alarms, and procedure overrides that raise mean time to recovery.
- A non-malicious misconfigured tool or testing script inadvertently generates malformed CIP frames; in an unsegmented network this can still produce widespread outages.
The common thread:
availability loss is immediate, visible, and operationally expensive. Even where no safety function is directly impacted by a single controller, the loss of telemetry and command capability impairs operator decision‑making and can force manual interventions.
Why Windows teams and IT managers at manufacturing sites must care
Many ICS architectures are hybrid: Windows servers host HMIs, historians, engineering tools and remote access gateways. When CompactLogix controllers fail, Windows‑hosted HMIs lose live I/O, historians stop receiving telemetry, and automated sequences may be interrupted. Ensuring PLCs remain reachable and predictable is therefore an IT priority as well as OT. The advisory explicitly connects to these cross‑domain effects and recommends IT/OT collaboration for mitigation planning and patching windows.
Strengths in the vendor and national response
- Timely coordination: Rockwell released a firmware update train and worked with national authorities to publish coordinated guidance, which helps operators plan remediation. The vendor-provided fixed versions are specific and distributed through normal vendor channels.
- Clear failure behavior: The advisory documents the fault mode and recovery path (manual restart), which aids incident response planning.
- Practical mitigations: The national advisory reiterates well‑tested ICS best practices: minimize exposure, segment the network, place devices behind firewalls, and use secure remote access methods like maintained VPNs or remote jump hosts.
- No public exploitation reported at publication: At the time of the advisory’s republication, there were no confirmed in‑the‑wild exploit reports targeting this specific CVE — but absence of evidence is not evidence of absence.
Risks, limitations, and potential blind spots
- Patching constraints in OT environments: Many facilities delay firmware changes due to uptime requirements, validation needs and change control processes. Where upgrade cycles are conservative, operators will rely on compensating controls — which increases exposure time.
- Attack proximity requirement can be misleading: The CVSS vector for this issue is AV:A (adjacent network), which implies the attacker needs closeness to the control network. However, misconfigured VPNs, weakly segmented enterprise‑to‑OT connectivity, and compromised engineering workstations can provide adjacency without requiring physical LAN access. Treat AV:A as a reduced barrier, not a guarantee of safety.
- Single‑point recovery cost: The need for a manual restart means outages may be prolonged in facilities with minimal overnight staffing or remote sites, increasing downtime exposure.
- Detection and telemetry gaps: Many sites lack fine‑grained CIP traffic logging or anomaly detection for EtherNet/IP sessions; without those, malformed forward open frames may go unnoticed until the device faults.
Recommended immediate actions — prioritized checklist
- Inventory and identify
- Record every CompactLogix 5370 unit in the estate: full model, firmware version, serial number, and network location.
- Confirm which units are on versions listed as vulnerable and classify them by criticality (safety critical, production‑critical, non critical).
- Patch where possible
- Schedule firmware upgrades to one of the fixed versions listed by Rockwell (37.011 or later; 34.016; 35.015; 36.012), following vendor guidance for staged testing and rollback procedures.
- If you cannot patch immediately — apply compensating controls
- Ensure control networks are segmented and inaccessible from the enterprise or Internet.
- Restrict adjacent network access to only trusted hosts and apply ACLs and host‑based firewall rules to block unauthorized CIP/EtherNet‑IP sessions.
- Disable unnecessary services and interfaces (e.g., restrict or disable remote management channels not in use).
- Harden VPN and remote access solutions: enforce multi‑factor authentication, limit the subnets reachable from remote sessions, and update VPN appliances to the latest security patches.
- Monitor and detect
- Increase logging of EtherNet/IP/CIP traffic at network choke points; look for malformed CIP forward open messages, unusual session patterns, or recurring connection resets.
- Correlate controller fault codes and LED indicators with network events to speed diagnosis. Vendor advisories often document specific fault codes or LED states to watch for.
- Prepare an operational recovery plan
- Ensure staff know the physical recovery steps required for an MNRF (who can perform manual restart, when, and what safety checks are necessary).
- Predefine communication protocols between OT teams and Windows‑hosted HMIs or supervisory layers to manage degraded visibility.
Detection guidance — practical indicators to watch for
- Unexpected Major Fault LEDs and fault codes on CompactLogix 5370 units immediately after CIP session establishment attempts.
- Sudden loss of telemetry or session resets on HMIs and historians coinciding with CIP forward open activity.
- Repeated failed or malformed CIP forward open messages in packet captures from OT network taps.
- Engineering‑workstation logs showing unauthorized or unexpected CIP tooling activity.
Implementing packet capture for a short observation window (carefully controlled) can reveal whether malformed session handling is present in the wild in your network.
Long‑term hardening and policy recommendations
- Adopt a strict network segmentation policy: put PLCs on dedicated VLANs with only the minimum necessary flows permitted (explicit allow rules).
- Enforce least privilege for remote access: use jump hosts and hardened management workstations rather than directly exposing engineering laptops to OT subnets.
- Centralize firmware and configuration management: maintain a vendor‑signed firmware repository and a test environment for validating updates before production rollout.
- Build incident playbooks that include physical actions (manual power‑cycle) and ensure on‑call staff are trained for night/weekend recovery scenarios.
- Run regular threat modeling for ICS assets, explicitly considering adjacent‑network attacks and misconfigured remote access as high‑probability vectors.
Vendor response: what to watch for and verify
When the vendor releases firmware, confirm the following before installation:
- The fixed firmware version exactly matches the vendor’s remediation table for your specific SKU.
- The vendor release notes list CVE‑CWE identifiers and describe the resolved fault condition.
- There are no new operational caveats or compatibility constraints introduced by the update.
- Where vendor guidance suggests migration paths for older hardware rather than firmware updates, evaluate long‑term replacement costs and timelines.
Administrators should also verify the firmware package integrity (digital signatures where provided) and follow change control approval processes that include functional validation on non‑production devices.
Critical analysis — balancing urgency, safety and operational continuity
Rockwell’s coordinated disclosure and the publishing of specific fixed firmware versions are positive: they provide an actionable remediation route. The clarity that the fault results from a malformed CIP forward open message — and that the result is availability loss requiring a restart — allows operators to craft precise detection rules and recovery procedures.
However, the realities of ICS operations complicate straightforward patching. The requirement for physical or manual restart after a fault implies downtime risks bigger than a simple software crash. Facilities operating 24/7 with limited on‑site staff may experience extended outages even when a fix is available; those sites must treat the advisory as high operational priority regardless of the CVSS numeric rating.
Another concern is the adjacency‑only vector: operators often assume that if devices are not Internet‑exposed they are safe. This advisory demonstrates why
adjacency — reachable via misconfigured VPNs, compromised jump hosts, or lax segmentation — can be as dangerous as remote Internet exposure. The real security control is strict segmentation and explicit allow lists, not a binary “Internet or not” view.
Detection and response playbook (quick reference)
- Immediately enumerate all CompactLogix 5370 units and their firmware.
- If any unit shows a vulnerable version, mark it critical and schedule testing for the fixed firmware.
- For high‑risk or production‑critical devices that cannot be patched quickly:
- Apply network ACLs to block CIP forward open requests from non‑trusted hosts.
- Restrict remote access subnets; require jump host access.
- Increase EtherNet/IP traffic logging for 72 hours and review for malformed forward open messages.
- Validate recovery procedures on a test rack: confirm manual restart steps, verify program integrity after restart, and document expected operator actions.
- Plan a staged firmware rollout: test → pilot → phased deployment with fallbacks.
Conclusion
CVE‑2025‑11743 in Rockwell Automation’s CompactLogix 5370 family highlights a familiar but serious pattern for ICS:
improper input validation in networked control protocols causes high‑impact availability failures. The vendor has supplied fixed firmware releases and national guidance emphasizes defense‑in‑depth. Immediate priorities are firm: inventory, prioritized patching where safe, compensating network controls where patching must wait, and clear operational recovery plans for major nonrecoverable faults.
For Windows teams and OT owners alike, this advisory is a reminder that protecting industrial environments requires both careful firmware lifecycle management and disciplined network architecture. Treat adjacency as a real attack surface, prioritize patch validation in staging, and ensure physical recovery steps are rehearsed and documented. Coordinated action now will reduce the chance that a single malformed CIP message becomes an extended production outage.
Source: CISA
Rockwell Automation CompactLogix 5370 | CISA