CVE-2026-4930

Executive Summary

CVE-2026-4930 describes a vulnerability in the SYMCRYPTO hardware engine, which is the host-side cryptographic accelerator for the SiXG301 device, accessed via the PSA Crypto library. The flaw allows an attacker with code execution on the device to weaken the Differential Power Analysis (DPA) countermeasures by forcing specific seed values. This reduction in entropy makes cryptographic keys loaded into SYMCRYPTO more susceptible to extraction through DPA side-channel attacks. The vulnerability is currently unpatched, and no public proof-of-concept or exploit code is available. The impact is limited to devices where an attacker has already achieved code execution, but the consequence is a severe compromise of key confidentiality.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating that no official CVSS vector has been assigned by NVD. However, based on the technical description, a reasonable assessment would be:

• Attack Vector (AV): Local (L) – Requires code execution on the device.
• Attack Complexity (AC): High (H) – Requires precise power analysis and seed manipulation.
• Privileges Required (PR): High (H) – Attacker must have code execution.
• User Interaction (UI): None (N) – No user action needed beyond initial compromise.
• Scope (S): Changed (C) – The attack impacts the confidentiality of keys beyond the attacker’s initial access.
• Confidentiality (C): High (H) – Keys can be extracted.
• Integrity (I): None (N) – No integrity impact.
• Availability (A): None (N) – No availability impact.

Estimated CVSS:3.1 Vector: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:N
Estimated Base Score: 5.3 (Medium)

Threat Level: Medium. The attack requires prior code execution, but the potential for key extraction makes it a serious concern for high-security deployments.

Deep Dive & Mechanics

The SYMCRYPTO engine is a hardware block designed to accelerate symmetric cryptographic operations (AES encryption/decryption and hashing) on the SiXG301 host side. It is accessed through the PSA (Platform Security Architecture) Crypto API. To protect against Differential Power Analysis (DPA) attacks, the engine employs countermeasures that introduce randomness (entropy) into the power consumption traces, making it difficult for an attacker to correlate power fluctuations with key bits.

The vulnerability lies in the seed generation mechanism for these DPA countermeasures. If an attacker gains code execution on the device (e.g., through a separate vulnerability), they can manipulate the seed values used by the countermeasure logic. By forcing specific, low-entropy seeds, the attacker reduces the effectiveness of the DPA protection. This allows the attacker to perform a more straightforward power analysis attack on the cryptographic operations, potentially extracting the secret keys loaded into the SYMCRYPTO engine.

The attack chain is:

1. Initial Compromise: Attacker exploits another vulnerability (e.g., buffer overflow, insecure API) to gain arbitrary code execution on the SiXG301 device.
2. Seed Manipulation: The attacker’s code interacts with the SYMCRYPTO control registers or memory-mapped I/O to force specific seed values for the DPA countermeasure random number generator.
3. Key Extraction: The attacker then performs a DPA attack on the cryptographic operations (e.g., AES encryption) while the weakened countermeasures are active. The reduced entropy makes the power traces more correlated with the key bits, allowing the attacker to recover the key.

Vulnerable vs. Patched Code

No specific code snippets are available for this vulnerability. The issue is in the hardware/firmware logic of the SYMCRYPTO engine. A patched version would likely involve:

• Vulnerable: The DPA countermeasure seed is writable by software without proper access control or validation.
• Patched: The seed is either hardcoded in hardware, generated by a dedicated hardware random number generator (TRNG) that cannot be influenced by software, or the write access is restricted to a secure enclave or privileged mode only.

Exploitation & Lab Setup

Red Team

Objective: Simulate the exploitation of CVE-2026-4930 to extract an AES key from a SiXG301 device.

Prerequisites:

• A SiXG301 development board or emulator.
• A power analysis tool (e.g., ChipWhisperer, PicoScope).
• A known vulnerability to gain code execution (e.g., a custom firmware with a debug backdoor).

Steps:

1. Gain Code Execution: Use a separate exploit (e.g., a buffer overflow in a network service) to execute arbitrary code on the device.
2. Identify SYMCRYPTO Registers: Reverse-engineer the device’s memory map to find the registers controlling the DPA countermeasure seed. This may require datasheets or firmware analysis.
3. Force Seed Value: Write a specific, low-entropy seed (e.g., all zeros) to the seed register.
4. Trigger Cryptographic Operation: Initiate an AES encryption operation using a known plaintext and the target key.
5. Capture Power Traces: Use the power analysis tool to capture power consumption traces during the AES operation.
6. Perform DPA: Use a tool like ChipWhisperer’s Jupyter notebooks or custom Python scripts to perform a DPA attack. The weakened countermeasures will make the correlation peaks more pronounced, allowing key recovery.

Example Python Snippet (Conceptual):

import ctypes

# Assume we have a handle to the device memory
device_mem = ctypes.CDLL("./device_memory_access.so")

# Address of the DPA seed register (hypothetical)
DPA_SEED_ADDR = 0x4000_1000

# Force seed to zero
device_mem.write_word(DPA_SEED_ADDR, 0x00000000)

# Now trigger AES encryption
# ... (device-specific API calls)

Blue Team

Objective: Detect and prevent exploitation of CVE-2026-4930.

Detection:

• Monitor for unexpected writes to SYMCRYPTO control registers. This can be done via hardware performance counters or firmware hooks.
• Look for anomalous power consumption patterns that indicate a DPA attack in progress (e.g., repeated encryption of the same plaintext).
• Use a hardware security module (HSM) or secure enclave to manage keys, preventing direct access to SYMCRYPTO from untrusted code.

Prevention:

• Apply firmware updates that restrict write access to the DPA seed register to a secure bootloader or trusted execution environment (TEE).
• Implement runtime integrity checks on the SYMCRYPTO configuration.
• Use key wrapping or ephemeral keys to limit the impact of key extraction.

Indicators of Compromise (IOCs)

• Memory Write Patterns: Repeated writes to the SYMCRYPTO DPA seed register (e.g., address 0x4000_1000).
• Power Analysis Signatures: Unusual number of repeated cryptographic operations with the same key and plaintext.
• Firmware Anomalies: Unexpected code execution in the memory region responsible for SYMCRYPTO configuration.
• Log Entries: (If available) Logs indicating unauthorized access to hardware cryptographic accelerators.

Detection Engineering

YARA Rule

rule CVE_2026_4930_SYMCRYPTO_SEED_MANIPULATION {
    meta:
        description = "Detects attempts to manipulate SYMCRYPTO DPA seed registers"
        author = "Valters IT"
        date = "2025-04-14"
        cve = "CVE-2026-4930"
    strings:
        $seed_write = { 48 8B 05 ?? ?? ?? ?? 48 89 05 ?? ?? ?? ?? }  // mov rax, [rip+...]; mov [rip+...], rax (generic write pattern)
        $dpa_seed_addr = { 00 10 00 40 }  // Little-endian representation of 0x40001000
    condition:
        $seed_write and $dpa_seed_addr
}

Sigma Rule

title: CVE-2026-4930 SYMCRYPTO DPA Seed Manipulation
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects writes to the SYMCRYPTO DPA seed register, indicating potential exploitation of CVE-2026-4930.
author: Valters IT
date: 2025-04-14
logsource:
    product: linux
    service: sysmon
    category: process_access
detection:
    selection:
        EventID: 10  # Process access
        TargetObject|contains: '0x40001000'
    condition: selection
falsepositives:
    - Legitimate firmware updates that modify the seed register.
level: high

Suricata Rule

alert ip any any -> any any (msg:"CVE-2026-4930 SYMCRYPTO DPA Seed Write Attempt"; content:"|00 10 00 40|"; offset:0; depth:4; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate Affected Devices: If possible, disconnect SiXG301 devices from untrusted networks to reduce the attack surface.
2. Monitor for Code Execution: Implement strict application whitelisting and memory protection (e.g., W^X) to prevent arbitrary code execution.
3. Use Key Management Best Practices: Avoid loading long-term keys into SYMCRYPTO. Use session keys or key derivation functions to limit exposure.

Long-Term Fix:

• Vendor Patch: Await a firmware update from Symcrypto that restricts write access to the DPA seed register or uses a hardware TRNG that cannot be influenced by software.
• Hardware Revision: In future hardware revisions, ensure the DPA countermeasure seed is generated by a dedicated, non-writable hardware source.

Workaround:

• If the device supports it, disable the SYMCRYPTO engine and perform cryptographic operations in software using a side-channel resistant implementation (e.g., constant-time AES).

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert