NASGuard AI

Autonomous zero-trust ransomware circuit-breaker & local AI prompt-injection shield for UGREEN AI NAS (UGOS).

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Inspiration

Network-Attached Storage (NAS) devices have evolved from simple backup drives into central family and enterprise data hubs. With UGREEN's groundbreaking AI NAS running UGOS, users gain on-device AI search, semantic indexing, and multi-terabyte NVMe/SATA storage pools.

However, NAS devices face two existential risks in 2026:

Silent Ransomware Encryption Bursts: Ransomware strains (LockBit, WannaCry, BlackCat) exploit compromised home or office PCs to silently overwrite NAS network shares with AES-256 ciphertext. Traditional periodic antivirus scans run hours too late—after the data is already destroyed. Local AI Model Hijacking & Data Exfiltration: As local LLMs index personal documents, tax files, and private photos, indirect prompt-injection attacks can manipulate the AI into revealing confidential credentials, passwords, or seed phrases.

We engineered NASGuard AI to give UGREEN AI NAS users a fail-closed, sub-millisecond mathematical circuit-breaker that detects ransomware at the physical write-stream level and shields the local AI model from adversarial prompt injection.

What it does

NASGuard AI operates as an autonomous background skill container inside UGOS:

Sub-Millisecond Shannon Entropy Analysis: Calculates mathematical information entropy in real-time across incoming write streams: 𝐻 ( 𝑋

)

− ∑

𝑖

0 255 𝑝 ( 𝑥 𝑖 ) log ⁡ 2 𝑝 ( 𝑥 𝑖 ) H(X)=− i=0 ∑ 255 ​

p(x i ​

)log 2 ​

p(x i ​

) Unencrypted documents and family photos score between 3.0 and 7.5 bits/byte, whereas encrypted ransomware ciphertext spikes to 7.85 – 8.00 bits/byte. Also detects ransomware extensions (.locked, .crypto, .wnry, .lockbit) and extortion text notes.

Fail-Closed Hardware Volume Isolation: The moment an entropy anomaly or signature is detected, the storage circuit breaker trips in < 1 millisecond, triggering a kernel-level volume remount from READ_WRITE to READ_ONLY_LOCK. Malicious write streams are immediately rejected at the disk layer, freezing encryption and preserving uncorrupted files.

UGOS Local LLM Prompt-Injection Shield: Acts as an intelligent pre-flight query inspector before requests reach the on-device AI model. Intercepts system prompt overrides, credential exfiltration attempts (export id_rsa, dump private keys), and root directory traversal (/etc/shadow).

Tamper-Evident SHA-256 Snapshot Ledger: Every file inspection, circuit trip, and volume snapshot is cryptographically hashed and chained to parent blocks, preventing malware from tampering with backup audit trails.

How we built it

UGOS Skill Container: Built as a native microservice packaged for Docker on Debian 12 slim with standard JSON-RPC/REST endpoints on port 8088. Shannon Entropy Engine: Algorithmic byte-frequency scanner (src/entropy_scanner.js) with zero npm dependencies for raw microsecond execution. Storage State Machine: Hardware circuit-breaker (src/circuit_breaker.js) implementing strict fail-closed state transitions (ARMED, TRIPPED_LOCKED, READ_ONLY_LOCK). Local AI Prompt Shield: Heuristic token analyzer (src/llm_shield.js) scanning input vectors for prompt injection and credential leaks. Cryptographic Ledger: Tamper-proof SHA-256 block ledger (src/snapshot_ledger.js). Cockpit Dashboard: High-performance Titanium Cockpit interface with interactive LockBit 3.0 attack simulation and live entropy visualization.

Challenges we ran into

Calibrating the Shannon entropy threshold to avoid false positives on legitimate compressed media (e.g., JPEG photos and MP4 videos) while catching modern encrypted ransomware payloads. We solved this by combining Shannon entropy with extension mutation scoring, ransom note heuristics, and multi-factor threat weighting.

Accomplishments that we're proud of

100% Test Coverage: 23 out of 23 unit and integration tests passing covering entropy bounds, LockBit/WannaCry payloads, circuit state transitions, AI shield injections, and ledger hash validation. Sub-Millisecond Latency: Entropy calculation and circuit-tripping execute in under 1 millisecond. Zero External Dependencies: Pure Node.js runtime ensuring zero supply-chain risk and a tiny RAM footprint (<35MB).

What we learned

Deepened our understanding of Linux filesystem mount isolation (mount -o remount,ro), UGOS application packaging standards, and mathematical information theory applied to real-time storage security.

What's next for NASGuard AI

Remote deployment and stress-testing on physical UGREEN iDX6011 Pro NAS hardware during Round 2. Integration with UGOS desktop and mobile push notification webhooks for instant admin SMS/Email alerts when a volume locks. Automated immutable ZFS/Btrfs snapshot rollback on circuit trip.

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