[nightshift] Security Audit: Ancla

Codebase: Microck/ancla
Date: 2026-04-07
Auditor: Nightshift v3 (GLM 5.1) — automated static analysis
Scope: All Swift source files, entitlements, plists, CI workflows

Summary

Ancla is an iOS app that uses NFC physical tags as keys to lock and release Screen Time / app blocking sessions. It uses Apple's FamilyControls and ManagedSettings frameworks. No network communication occurs — this eliminates a large class of vulnerabilities. The primary attack surface is local data at rest and the integrity of stored session state.

Findings

1. Plaintext Storage of Sensitive Session State — P1 High

Files: ios/ancla-shared/ancla-store.swift:36-40, ios/ancla-lite/ancla-lite-support.swift:67-70
Category: Insecure data storage

The AppSnapshot — containing NFC tag hash fingerprints (uidHash), session authorization state (isAuthorized), emergency unbrick count, and full session history — is serialized as unencrypted, plaintext JSON to disk. Pretty-printed with sorted keys, making it easy to read and modify.

Fix: Encrypt using CryptoKit AES-GCM with a Keychain-stored key. Add NSFileProtectionComplete. Remove .prettyPrinted in production.

2. Emergency Unbrick Counter Tamperable — P1 High

Files: ios/ancla-shared/ancla-models.swift:212, ios/ancla-shared/ancla-store.swift:36-40
Category: Authorization bypass

emergencyUnbricksRemaining (default: 5) is a plain integer in the JSON snapshot. With filesystem access, the counter can be reset to any value, bypassing the physical NFC anchor requirement entirely.

Fix: Store in iOS Keychain with kSecAttrAccessibleWhenUnlockedThisDeviceOnly. Add HMAC over the snapshot.

3. No Integrity Verification on Stored Snapshot — P1 High

Files: ios/ancla-shared/ancla-store.swift:26-33, ios/ancla-lite/ancla-lite-support.swift:57-65
Category: Integrity / Tampering

Snapshot is decoded with JSONDecoder without integrity check. Attacker with write access could modify isAuthorized, activeSession.state, pairedTagId, or remove session history entries.

Fix: Compute HMAC-SHA256 using a Keychain-stored key. Verify before decoding. Reset on verification failure.

4. Shield Extension Reads Shared State Without Synchronization — P2 Medium

Files: ios/ancla-shield-extension/shield-configuration-extension.swift:6,31
Category: Race condition

ShieldConfigurationExtension instantiates its own AppGroupStore() and calls load() independently on every callback. No file locking or coordination with the main app's writes.

Fix: Use NSFileCoordinator/NSFilePresenter, or add a version/timestamp field.

5. NFC Tag Hash Partially Exposed in UI — P2 Medium

Files: ios/ancla-app/content-view.swift:1138-1142
Category: Privacy leak

First 4 and last 4 characters of the NFC tag's SHA-256 hash displayed in UI. Shoulder surfing or screenshots leak 32 bits of the authentication credential.

Fix: Replace with a non-reversible color swatch or shortened 3-char preview.

6. Session History Grows Without Bound — P2 Medium

Files: ios/ancla-shared/ancla-core.swift:138-160
Category: Data exposure / Resource exhaustion

sessionHistory entries appended with no pruning. Full history persists in plaintext JSON indefinitely.

Fix: Cap at 100 entries. Prune oldest on overflow.

7. Test Hash Injection via Environment Variable — P2 Medium

Files: ios/ancla-lite/ancla-lite-support.swift:30-46,100-111
Category: Authentication bypass in non-production builds

ANCLA_TEST_STICKER_HASHES env var injects arbitrary NFC tag hashes, completely bypassing the physical token. Debug builds on real devices are vulnerable.

Fix: Gate behind #if DEBUG in addition to env var check. Add runtime assertion for Release builds.

8. Sideload-Lite Build Bypasses All Authorization — P2 Medium

Files: ios/ancla-lite/ancla-lite-support.swift:86-90, ios/ancla-app/app-view-model.swift:201-204
Category: Authorization bypass by design

Sideload-lite build has no actual app blocking — LiteAuthorizationClient.request() is a no-op, auto-sets isAuthorized = true. Users may misunderstand the build variant.

Fix: Prominently distinguish lite build as "simulation only" in UI.

9. No File Protection Attributes on Stored Snapshot — P2 Medium

Files: ios/ancla-shared/ancla-store.swift:39, ios/ancla-lite/ancla-lite-support.swift:70
Category: Insecure data storage

Snapshot written without NSFileProtectionComplete. Files may be accessible when device is locked via forensic tools.

Fix: Set FileProtectionType.complete after writing.

10. App Group Identifier Hardcoded — P3 Low

Files: ios/ancla-shared/ancla-models.swift:4
Category: Information disclosure

group.dev.micr.ancla hardcoded in source. Low risk due to Apple provisioning, but any app can read on jailbroken devices.

11. StickerPairingService Continuation Edge Case — P3 Low

Files: ios/ancla-services.swift:72-177
Category: Memory safety

Manual CheckedContinuation management has theoretical edge case where post-invalidation processing could attempt to invalidate an already-invalidated NFC session.

Fix: Add explicit isFinished boolean guard.

Positive Findings

• CI workflows properly configured: secrets via secrets.*, least-privilege permissions, chmod 600 on API keys, concurrency groups.
• Zero network communication: no analytics, telemetry, or API calls. Eliminates MITM, data exfiltration, and SSL/TLS vectors.
• No hardcoded secrets found in the repository.

Severity Summary

Top Priority

Encrypt the snapshot at rest — addresses findings #1, #2, #3, and partially #5 and #9 in a single fix. Use CryptoKit AES-GCM with Keychain-stored key + HMAC integrity verification.