CVE-2026-54799

Executive Summary

CVE-2026-54799 is a critical vulnerability in Siemens CPCI85 Central Processing/Communication and SICORE Base system firmware. The flaw resides in the firmware update mechanism's signature validation process, allowing an attacker with high privileges to install malicious firmware. Successful exploitation leads to persistent code execution and full system compromise. The vulnerability has a CVSS score of 6.7 (Medium), but its impact is severe due to the potential for long-term persistence and control over critical industrial communication systems. No public exploit code or proof-of-concept is currently available, and the EPSS score is 0.0%, indicating low exploitation activity in the wild. The vendor has not released a patch, but recommends upgrading to the latest versions.

CVSS Breakdown & Threat Level

• CVSS Score: 6.7 (Medium)
• Vector: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
• Attack Vector (AV): Local (L) – Requires physical or logical access to the device.
• Attack Complexity (AC): High (H) – Exploitation requires specific conditions or knowledge.
• Privileges Required (PR): High (H) – Attacker needs administrative privileges.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Vulnerability does not affect other components.
• Confidentiality (C): High (H) – Full data compromise.
• Integrity (I): High (H) – Full system integrity loss.
• Availability (A): High (H) – Full system availability loss.

Threat Level: Medium (due to high privileges required, but severe impact if exploited).

Deep Dive & Mechanics

The vulnerability exists in the firmware update mechanism of CPCI85 and SICORE systems. The signature validation process fails to properly verify the authenticity and integrity of firmware images before installation. This allows an attacker with high privileges (e.g., root access) to replace legitimate firmware with a malicious version.

Attack Flow:

1. Privilege Escalation: Attacker gains high privileges on the device (e.g., via another vulnerability or physical access).
2. Firmware Preparation: Attacker crafts a malicious firmware image with a forged or invalid signature.
3. Bypass Validation: The flawed signature validation accepts the malicious firmware.
4. Installation: The malicious firmware is installed, overwriting the legitimate firmware.
5. Persistence: The malicious firmware persists across reboots, giving the attacker persistent code execution and control.

Impact: Full system compromise, including data exfiltration, lateral movement, and disruption of industrial processes.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// Vulnerable signature validation
int validate_firmware_signature(firmware_image *img) {
    // Weak or missing validation
    if (img->signature == NULL) {
        return 1; // Accept unsigned firmware
    }
    // No cryptographic verification
    return 1; // Always accept
}

Patched Code (Conceptual):

// Patched signature validation
int validate_firmware_signature(firmware_image *img) {
    // Strong cryptographic verification
    if (!verify_ecdsa_signature(img->data, img->size, img->signature, trusted_public_key)) {
        return 0; // Reject invalid signature
    }
    return 1; // Accept only valid signatures
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• High privileges on the target device (root or admin).
• Physical or logical access to the device's firmware update interface.
• Knowledge of the firmware image format.

Exploitation Steps:

1. Gain Access: Use another vulnerability or physical access to obtain root shell.
2. Extract Firmware: Dump the current firmware for analysis.
3. Craft Malicious Firmware: Modify the firmware to include a backdoor or persistence mechanism.
4. Bypass Validation: Exploit the weak signature validation to install the malicious firmware.
5. Trigger Update: Use the device's update mechanism to install the malicious firmware.
6. Verify Persistence: Reboot the device and confirm the malicious firmware is active.

Example Command (Conceptual):

# Assuming root access and a custom firmware image
cp malicious_firmware.bin /tmp/firmware.bin
echo "update_firmware /tmp/firmware.bin" > /proc/firmware_control

Blue Team (Detection & Defense)

Detection:

• Monitor for unauthorized firmware update attempts.
• Log all firmware update operations and verify signatures.
• Use integrity monitoring tools (e.g., AIDE, Tripwire) to detect firmware changes.

Defense:

• Restrict physical access to devices.
• Implement strict access controls and least privilege.
• Enable secure boot and trusted platform module (TPM) if available.
• Regularly audit firmware versions and signatures.

Indicators of Compromise (IOCs)

• File Hashes: (Example – replace with actual hashes if available)
  • malicious_firmware.bin SHA256: a1b2c3d4e5f6...
• Network Indicators:
  • Unusual outbound connections from the device to unknown IPs.
  • Firmware update traffic from unexpected sources.
• System Indicators:
  • Unexpected firmware version or build date.
  • Presence of unauthorized files in /boot or firmware partitions.
  • Modified system binaries or kernel modules.
• Log Indicators:
  • Firmware update logs without proper authentication.
  • Signature validation failures (if logging is enabled).

Detection Engineering

YARA Rule

rule CVE_2026_54799_Malicious_Firmware {
    meta:
        description = "Detects malicious firmware images exploiting CVE-2026-54799"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-54799"
    strings:
        $s1 = "CPCI85" ascii wide nocase
        $s2 = "SICORE" ascii wide nocase
        $s3 = { 00 00 00 00 } // Placeholder for weak signature pattern
    condition:
        all of ($s*) and filesize < 10MB
}

Sigma Rule

title: Firmware Update Anomaly Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects suspicious firmware update attempts on CPCI85/SICORE devices
author: Valters IT
date: 2026-01-01
references:
    - https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-54799
logsource:
    product: linux
    service: syslog
detection:
    selection:
        - "firmware update initiated"
        - "signature validation failed"
        - "unauthorized firmware"
    condition: selection
falsepositives:
    - Legitimate firmware updates
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-54799 - Malicious Firmware Download"; flow:to_server; content:"|00 00 00 00|"; depth:4; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Firmware: Update to CPCI85 V26.20 or SICORE V26.20.0.
2. Restrict Access: Limit physical and logical access to devices.
3. Enable Logging: Ensure firmware update operations are logged and monitored.

Long-Term Measures:

1. Implement Secure Boot: Use hardware-based secure boot to verify firmware integrity.
2. Code Signing: Enforce strict cryptographic signature verification for all firmware updates.
3. Regular Audits: Conduct periodic security audits of firmware and system integrity.
4. Network Segmentation: Isolate critical devices from untrusted networks.

Workarounds:

• If upgrade is not possible, disable firmware update functionality if not required.
• Use network-based intrusion detection to monitor for exploitation attempts.

Valters IT