CVE-2025-11781: Circutor SGE-PLC Auth Bypass Vulnerability

CVE-2025-11781 Overview

CVE-2025-11781 is a hardcoded cryptographic key vulnerability affecting Circutor SGE-PLC1000 and SGE-PLC50 industrial devices running firmware version 9.0.2. The firmware embeds a static authentication key that protects firmware update packages. An attacker with local access to the device can recover this key through firmware image analysis or memory inspection. Once extracted, the key allows the attacker to forge valid firmware update packages, bypass access controls, and gain full administrative privileges on the device. The flaw is tracked under CWE-321: Use of Hard-coded Cryptographic Key.

Critical Impact
Recovery of the hardcoded key enables attackers to sign malicious firmware update packages and obtain full administrative control over affected Circutor SGE-PLC devices.

Affected Products

Circutor SGE-PLC1000 (firmware version 9.0.2)
Circutor SGE-PLC50 (firmware version 9.0.2)
Circutor SGE-PLC1000 and SGE-PLC50 hardware platforms

Discovery Timeline

2025-12-02 - CVE-2025-11781 published to NVD
2025-12-03 - Last updated in NVD database

Technical Details for CVE-2025-11781

Vulnerability Analysis

The Circutor SGE-PLC1000 and SGE-PLC50 are power line communication devices used in industrial energy management and smart grid environments. Firmware 9.0.2 ships with a hardcoded static authentication key embedded directly in the firmware binary. This key is used to validate firmware update packages presented to the device.

Because the same key is shared across every deployed unit, recovery on a single device compromises the entire product line. An attacker who obtains physical or local access to one unit can extract the key from flash storage, a memory dump, or by reverse engineering the firmware image. The attacker can then craft signed firmware images accepted by any vulnerable device, regardless of vendor authorization.

Root Cause

The root cause is the inclusion of a static cryptographic secret inside distributed firmware images, classified as CWE-321: Use of Hard-coded Cryptographic Key. Secure firmware update designs rely on per-device keys, asymmetric signing with vendor-held private keys, or hardware security modules. Storing a shared symmetric secret in firmware violates this principle because every customer with a firmware image effectively possesses the verification secret.

Attack Vector

Exploitation requires local access to the target device or to a firmware image. The workflow consists of three stages. First, the attacker acquires a copy of the firmware, either from the vendor download portal or by reading flash memory on a physical unit. Second, the attacker locates the embedded key inside the binary using string searches, entropy analysis, or by tracing the update verification routine. Third, the attacker builds a malicious firmware package, computes the authentication value using the recovered key, and uploads it through the standard update interface. The device accepts the package as legitimate and installs attacker-controlled code with administrative privileges.

No verified public proof-of-concept code is available for CVE-2025-11781. See the INCIBE CERT Vulnerability Notice for vendor coordination details.

Detection Methods for CVE-2025-11781

Indicators of Compromise

Unexpected firmware version strings or build identifiers reported by SGE-PLC1000 or SGE-PLC50 devices after maintenance windows.
Firmware update events originating from unmanaged hosts, engineering laptops, or addresses outside the asset management network.
Configuration changes, new administrative accounts, or altered network parameters appearing on PLC devices without a corresponding change ticket.

Detection Strategies

Maintain a baseline of authorized firmware hashes for each Circutor model and alert when computed hashes deviate after an update.
Inspect device system logs for firmware upload activity, focusing on the source address, timestamp, and uploaded image identifier.
Correlate physical access events at substations or industrial cabinets with PLC firmware update timestamps to surface unauthorized local interactions.

Monitoring Recommendations

Forward syslog and SNMP trap data from SGE-PLC devices into a central SIEM or data lake for retention and correlation.
Monitor north-south and east-west traffic to the operational technology segment for unusual file transfers targeting PLC management ports.
Audit administrative logons to PLC web and console interfaces on a recurring schedule and review credential changes between audits.

How to Mitigate CVE-2025-11781

Immediate Actions Required

Inventory all Circutor SGE-PLC1000 and SGE-PLC50 units and confirm which run firmware 9.0.2 or earlier.
Restrict physical access to affected devices and the cabinets, panels, and substations housing them.
Segment the operational technology network so that only designated engineering workstations can reach PLC management interfaces.
Contact Circutor support to obtain patched firmware and authorized update procedures.

Patch Information

No fixed firmware version is documented in the NVD entry at publication. Refer to the INCIBE CERT Vulnerability Notice for the most current vendor remediation status and coordinated disclosure information.

Workarounds

Disable or block remote firmware update functionality on the device management network until patched firmware is deployed.
Enforce access control lists on switches and firewalls so that only authorized engineering workstations can initiate firmware updates.
Require multi-person authorization and change tickets for any firmware update on production PLC units, and verify image hashes against vendor-published values.
Increase logging and physical inspection cadence for substations until the issue is remediated.

bash

# Configuration example: restrict access to PLC management interface
# Replace <PLC_IP> and <ENGINEERING_WS_IP> with your asset addresses
iptables -A FORWARD -s <ENGINEERING_WS_IP> -d <PLC_IP> -p tcp --dport 443 -j ACCEPT
iptables -A FORWARD -d <PLC_IP> -j DROP