CVE-2026-3631 Overview
CVE-2026-3631 is an out-of-bounds read vulnerability [CWE-125] affecting Delta Electronics COMMGR2. The flaw allows a remote, unauthenticated attacker to trigger a buffer over-read condition that leads to denial of service (DoS). COMMGR2 is industrial software used to manage communications with Delta programmable logic controllers (PLCs), making availability impact relevant to operational technology (OT) environments.
Critical Impact
A remote attacker can crash the COMMGR2 service over the network without authentication or user interaction, disrupting PLC communications and dependent industrial processes.
Affected Products
- Delta Electronics COMMGR2 (see vendor advisory for fixed versions)
- Deployments using commgr2 as the PLC communication manager
- Industrial control environments relying on COMMGR2 for Delta PLC connectivity
Discovery Timeline
- 2026-03-09 - CVE-2026-3631 published to the National Vulnerability Database (NVD)
- 2026-03-10 - Last updated in NVD database
Technical Details for CVE-2026-3631
Vulnerability Analysis
The vulnerability is classified as an out-of-bounds read [CWE-125] in Delta Electronics COMMGR2. When the application processes specifically crafted input, it reads memory beyond the boundaries of an allocated buffer. The over-read condition causes the process to terminate, producing a denial of service against the COMMGR2 service.
Because COMMGR2 mediates communication with Delta PLCs, a crash interrupts engineering workstation interactions with field devices. In environments where COMMGR2 runs continuously to support project upload, monitoring, or simulation, repeated exploitation can prevent operators from maintaining visibility into PLC state.
The attack does not yield code execution or data exposure. The CVSS vector reflects an availability-only impact, with no confidentiality or integrity compromise.
Root Cause
The root cause is missing or insufficient bounds checking when COMMGR2 parses attacker-controlled data. The function handling the affected message processes a length or offset value without validating it against the actual buffer size, allowing reads past the buffer boundary. The resulting access violation terminates the process.
Attack Vector
Exploitation requires network reachability to the COMMGR2 host. An attacker sends a malformed packet to the listening service to trigger the over-read. No credentials, prior access, or user interaction is required. The vendor advisory describes the affected protocol handling and provides remediation guidance.
The vulnerability mechanism is described in prose only because no verified public proof-of-concept code is available. Refer to the Delta Security Advisory CVE-2026-3630/3631 for vendor-supplied technical details.
Detection Methods for CVE-2026-3631
Indicators of Compromise
- Unexpected termination or repeated restarts of the COMMGR2 process on engineering workstations
- Loss of communication between COMMGR2 and Delta PLCs without corresponding network outages
- Inbound traffic to COMMGR2 listening ports from unexpected or external hosts
Detection Strategies
- Monitor process lifecycle events for COMMGR2.exe crashes and Windows Error Reporting entries
- Inspect network traffic for malformed packets directed at COMMGR2 service ports
- Correlate PLC connectivity loss events with host-level service termination on COMMGR2 systems
Monitoring Recommendations
- Forward endpoint process and crash telemetry from engineering workstations to a centralized SIEM or data lake for correlation
- Baseline normal COMMGR2 network peers and alert on connections from outside the engineering network segment
- Track Windows event IDs related to application faults on hosts running COMMGR2
How to Mitigate CVE-2026-3631
Immediate Actions Required
- Inventory all hosts running Delta Electronics COMMGR2 and identify their network exposure
- Apply the vendor-supplied update referenced in Delta-PCSA-2026-00005 as soon as it is available for your version
- Restrict network access to COMMGR2 hosts so only authorized engineering workstations can reach the service
Patch Information
Delta Electronics has published advisory Delta-PCSA-2026-00005 covering CVE-2026-3630 and CVE-2026-3631. Refer to the Delta Security Advisory for fixed versions and upgrade instructions. Apply the patched COMMGR2 release on every affected engineering workstation.
Workarounds
- Place COMMGR2 hosts behind firewall rules that block inbound traffic from untrusted networks, following ISA/IEC 62443 zone and conduit guidance
- Run COMMGR2 only when actively required for PLC engineering tasks and stop the service otherwise
- Use host-based firewalls to limit COMMGR2 listeners to loopback or known peer IP addresses until the patch is applied
# Example Windows Firewall rule restricting COMMGR2 inbound traffic to a specific engineering host
netsh advfirewall firewall add rule name="COMMGR2 Restrict" dir=in action=block program="C:\Program Files\Delta Industrial Automation\COMMGR2\COMMGR2.exe" enable=yes
netsh advfirewall firewall add rule name="COMMGR2 Allow Engineering Host" dir=in action=allow program="C:\Program Files\Delta Industrial Automation\COMMGR2\COMMGR2.exe" remoteip=10.10.10.25 enable=yes
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
