registry / amicus / 1.7.3

amicus@1.7.3

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AI Security Review

scanned 3d ago · by lpm-firewall-ai

The package mutates Claude/AI-agent control surfaces during npm postinstall. It installs package-supplied skills and registers an MCP server that runs amicus via npx.

Static reason

High-risk behavior combination matched malicious policy.; previous stored version diff introduced dangerous source

Trigger

npm install running package postinstall

Impact

Persistent Claude skill/MCP configuration can route future AI-agent actions through package-controlled instructions and server code.

Mechanism

unconsented AI-agent skill and MCP registration

Attack narrative

On installation, scripts/postinstall.js runs automatically. It copies bundled Claude skills into the user's ~/.claude skill directories and registers amicus/sidecar MCP servers via the Claude CLI or direct Claude config-file edits. The MCP entry executes npx -y amicus@latest mcp, so later Claude sessions can invoke package-controlled code and instructions without the user separately running the CLI setup.

Rationale

Direct source inspection confirms automatic postinstall mutation of Claude skills and MCP configuration, which matches unconsented AI-agent control-surface mutation. Other risky primitives inspected, including Electron repair and credential loading, appear package-aligned and do not add confirmed exfiltration behavior. Product guard normalized a non-low false-positive publish_block request to warn-only suspicious.

Evidence

package.jsonscripts/postinstall.jssrc/sidecar/electron-install.jsbin/amicus.js~/.claude/skills/sidecar/SKILL.md~/.claude/skills/second-opinion/SKILL.md~/.claude/skills/second-opinion/COUNCIL-DESIGN.md~/.claude/skills/second-opinion/MODEL-NOTES.md~/.claude.json~/Library/Application Support/Claude/claude_desktop_config.json%APPDATA%/Claude/claude_desktop_config.json~/.config/claude/claude_desktop_config.json

Decision evidence

public snapshot

AI called this Suspicious at 90.0% confidence as Dangerous Capability with medium false-positive risk.

Evidence for block

package.json defines postinstall: node scripts/postinstall.js.
scripts/postinstall.js copies package skills into ~/.claude/skills/sidecar and ~/.claude/skills/second-opinion at install time.
scripts/postinstall.js registers MCP servers in Claude Code/Desktop configs, falling back to writes to ~/.claude.json and claude_desktop_config.json.
Registered MCP command is npx -y amicus@latest mcp, giving the package an AI-agent tool/control surface after install.
postinstall invokes claude mcp add-json when available, modifying user-scoped Claude Code configuration without an explicit runtime command.

Evidence against

Postinstall setup is documented in comments and logs, and failures are non-fatal.
Electron provisioning defaults to cache-only; networked Electron prewarm requires AMICUS_PREFETCH_ELECTRON=1.
bin/amicus.js credential loading appears tied to CLI operation, not automatic exfiltration.
No credential harvesting or exfiltration endpoint was confirmed in inspected files.

Behavioral surface

Source

ChildProcessCryptoDynamicRequireEnvironmentVarsFilesystemNetwork

Supply chain

HighEntropyStringsUrlStrings

ManifestNo manifest risk signals triggered.

scanned 117 file(s), 714 KB of source, external domains: aistudio.google.com, api.anthropic.com, api.deepseek.com, api.openai.com, console.anthropic.com, generativelanguage.googleapis.com, nodejs.org, openrouter.ai, platform.deepseek.com, platform.openai.com, www.w3.org

Source & flagged code

5 flagged

package.jsonView file

Lines 36-76json

36 "./opencode-client": "./src/opencode-client.mjs"

37 },

38 "files": [

39 "bin/",

40 "src/",

41 "electron/",

42 "skills/",

43 ".claude-plugin/",

44 "CHANGELOG.md",

45 "scripts/postinstall.js",

46 "scripts/setup-hooks.js"

47 ],

48 "scripts": {

49 "start": "node --experimental-top-level-await --experimental-vm-modules bin/amicus.js",

50 "test": "jest",

51 "test:integration": "jest --testPathIgnorePatterns='\\.worktrees/' --testMatch='**/tests/**/*.integration.test.js'",

52 "test:all": "jest --testPathIgnorePatterns='/node_modules/' --testPathIgnorePatterns='\\.worktrees/' && node scripts/mark-test-passed.js",

53 "test:e2e:mcp": "jest tests/mcp-repomix-e2e.integration.test.js --testTimeout=180000 --forceExit",

54 "posttest": "node scripts/mark-test-passed.js",

55 "lint": "eslint src/",

56 "postinstall": "node scripts/postinstall.js",

High

Install Time Lifecycle Scripts

Package defines install-time lifecycle scripts.

package.jsonView on unpkg · L56

Medium

Ambiguous Install Lifecycle Script

Install-time lifecycle script is not statically allowlisted and needs review.

package.jsonView on unpkg · L56

57 "test:thinking": "node scripts/benchmark-thinking.js",

58 "test:thinking:quick": "MODELS=gemini node scripts/benchmark-thinking.js",

59 "refresh-models": "node bin/amicus.js models --refresh",

60 "models:info": "node bin/amicus.js models",

61 "models:check": "node bin/amicus.js models --check",

62 "generate-icon": "node scripts/generate-icon.js",

63 "generate-docs": "node scripts/generate-docs.js",

64 "generate-docs:check": "node scripts/generate-docs.js --check",

65 "validate-docs": "node scripts/validate-docs.js --full",

66 "setup-hooks": "node scripts/setup-hooks.js",

67 "check:secrets": "node scripts/check-secrets.js --all",

68 "check:sizes": "node scripts/check-file-sizes.js --all",

69 "check:tarball": "node scripts/check-tarball-lifecycle.js"

70 },

71 "dependencies": {

72 "@modelcontextprotocol/sdk": "^1.27.0",

73 "@opencode-ai/sdk": "^1.1.36",

74 "dotenv": "^17.2.3",

75 "opencode-ai": "^1.2.20",

76 "tiktoken": "^1.0.0",

bin/amicus.jsView file

Lines 1-33javascript

1#!/usr/bin/env node

3/**

4 * Amicus CLI Entry Point

5 *

6 * Spec Reference: §4 CLI Interface

7 * Routes commands to appropriate handlers.

8 */

10// One-time, non-destructive migration of the legacy ~/.config/sidecar dir onto

11// the canonical ~/.config/amicus (copy; legacy kept as a backup). Runs before

12// any config/credential read so both resolve to the unified dir. Best-effort.

13try {

14 const { migrateLegacyConfigDir } = require('../src/utils/config');

15 const _m = migrateLegacyConfigDir();

Medium

Dynamic Require

Package source references dynamic require/import behavior.

bin/amicus.jsView on unpkg · L13

16 if (_m && _m.migrated) {

17 process.stderr.write(`[amicus] Migrated config ${_m.from} → ${_m.to} (legacy kept as a backup).\n`);

18 }

19} catch { /* best-effort: never block startup on migration */ }

21// Load API keys from all sources: process.env > sidecar .env > auth.json

22const { loadCredentials } = require('../src/utils/env-loader');

23loadCredentials();

25const { parseArgs, getUsage } = require('../src/cli');

26const { validateTaskId } = require('../src/utils/validators');

27const { resolveModelFromArgs, validateFallbackModel } = require('../src/utils/start-helpers');

28const { handleSetup, handleAbort, handleUpdate, handleMcp, handleKey } = require('../src/cli-handlers');

29const { handleStart, handleFanout, handleRead } = require('../src/cli-handlers-run');

30const { isOneShotCommand, armExitWatchdog } = require('../src/utils/lifecycle');

31const { logger } = require('../src/utils/logger');

33const VERSION = require('../package.json').version;

scripts/postinstall.jsView file

Lines 1-25javascript

1#!/usr/bin/env node

3/**

4 * Post-install script for amicus

5 *

6 * 1. Copies SKILL.md to ~/.claude/skills/sidecar/

7 * 2. Registers MCP server in Claude Code (~/.claude.json)

8 * 3. Registers MCP server in Claude Desktop/Cowork config

9 */

11const fs = require('fs');

12const path = require('path');

13const os = require('os');

Critical

Ai Agent Control Hijack

Install-time source drops package-supplied AI-agent/MCP control files or instructions.

scripts/postinstall.jsView on unpkg · L5

14const { execFileSync } = require('child_process');

16const { repairElectron } = require('../src/sidecar/electron-install');

17const HINTS = require('../src/utils/remediation-hints');

19const SETUP_HOOKS_SCRIPT = path.join(__dirname, 'setup-hooks.js');

21/** Short cache-only provision budget: a slow disk must never hang the install. */

22const PROVISION_TIMEOUT_MS = 15000;

24const SKILL_SOURCE = path.join(__dirname, '..', 'skills', 'sidecar', 'SKILL.md');

25const COUNCIL_SOURCE_DIR = path.join(__dirname, '..', 'skills', 'second-opinion');

src/sidecar/electron-install.jsView file

•matchType = previous_version_dangerous_delta matchedPackage = amicus@1.7.2 matchedIdentity = npm:YW1pY3Vz:1.7.2 similarity = 0.991 summary = stored previous version shares package body but lacks this dangerous source file

Critical

Previous Version Dangerous Delta

This package version adds a dangerous source file absent from the previous stored version.

src/sidecar/electron-install.jsView on unpkg

Source & flagged code

5 flagged · loading source

package.jsonView file

•scripts.postinstall = node scripts/postinstall.js

High

Install Time Lifecycle Scripts

Package defines install-time lifecycle scripts.

package.jsonView on unpkg

•scripts.postinstall = node scripts/postinstall.js

Medium

Ambiguous Install Lifecycle Script

Install-time lifecycle script is not statically allowlisted and needs review.

package.jsonView on unpkg

bin/amicus.jsView file

13try { L14: const { migrateLegacyConfigDir } = require('../src/utils/config'); L15: const _m = migrateLegacyConfigDir();

Medium

Dynamic Require

Package source references dynamic require/import behavior.

bin/amicus.jsView on unpkg · L13

scripts/postinstall.jsView file

5Install-time AI-agent control hijack evidence: L5: * L6: * 1. Copies SKILL.md to ~/.claude/skills/sidecar/ L7: * 2. Registers MCP server in Claude Code (~/.claude.json) L8: * 3. Registers MCP server in Claude Desktop/Cowork config ... L36: function skillsRoot() { L37: return path.join(os.homedir(), '.claude', 'skills'); L38: } ... L58: L59: if (!existing.mcpServers) { existing.mcpServers = {}; } L60: L61: const prev = existing.mcpServers[name]; L62: const status = !prev ? 'added' : JSON.stringify(prev) !== JSON.stringify(config) ? 'updated' : 'unchanged'; Payload evidence from skills/sidecar/SKILL.md: L11: run_in_background: true. Never run amicus start/resume/continue in the foreground. L12: (2) The fold summary returns on stdout when the user clicks Fold in the GUI or the L13: headless agent finishes. Use TaskOutput to read it when the background task completes. ... L69: **Step 1: Get an OpenRouter API key** L70: - Sign up at https://openrouter.ai L71: - Go to Keys → Create Key ... L78: mkdir -p ~/.local/share/opencode L79: cat > ~/.local/share/opencode/auth.json << 'EOF' L80: { ... L119: L120: Add these to your shell profile (`~/.bashrc`, `~/.zshrc`) for persistence. L121:

Critical

Ai Agent Control Hijack

Install-time source drops package-supplied AI-agent/MCP control files or instructions.

scripts/postinstall.jsView on unpkg · L5

src/sidecar/electron-install.jsView file

Critical

Previous Version Dangerous Delta

This package version adds a dangerous source file absent from the previous stored version.

src/sidecar/electron-install.jsView on unpkg

Findings

2 Critical1 High5 Medium4 Low

CriticalAi Agent Control Hijackscripts/postinstall.js

CriticalPrevious Version Dangerous Deltasrc/sidecar/electron-install.js

HighInstall Time Lifecycle Scriptspackage.json

MediumAmbiguous Install Lifecycle Scriptpackage.json

MediumDynamic Requirebin/amicus.js

MediumNetwork

MediumEnvironment Vars

MediumStructural Risk Force Deep Review

LowScripts Present

LowFilesystem

LowHigh Entropy Strings

LowUrl Strings

Source & flagged code

5 flagged

package.jsonView file

Lines 36-76json

36 "./opencode-client": "./src/opencode-client.mjs"

37 },

38 "files": [

39 "bin/",

40 "src/",

41 "electron/",

42 "skills/",

43 ".claude-plugin/",

44 "CHANGELOG.md",

45 "scripts/postinstall.js",

46 "scripts/setup-hooks.js"

47 ],

48 "scripts": {

49 "start": "node --experimental-top-level-await --experimental-vm-modules bin/amicus.js",

50 "test": "jest",

51 "test:integration": "jest --testPathIgnorePatterns='\\.worktrees/' --testMatch='**/tests/**/*.integration.test.js'",

52 "test:all": "jest --testPathIgnorePatterns='/node_modules/' --testPathIgnorePatterns='\\.worktrees/' && node scripts/mark-test-passed.js",

53 "test:e2e:mcp": "jest tests/mcp-repomix-e2e.integration.test.js --testTimeout=180000 --forceExit",

54 "posttest": "node scripts/mark-test-passed.js",

55 "lint": "eslint src/",

56 "postinstall": "node scripts/postinstall.js",

High

Install Time Lifecycle Scripts

Package defines install-time lifecycle scripts.

package.jsonView on unpkg · L56

Medium

Ambiguous Install Lifecycle Script

Install-time lifecycle script is not statically allowlisted and needs review.

package.jsonView on unpkg · L56

57 "test:thinking": "node scripts/benchmark-thinking.js",

58 "test:thinking:quick": "MODELS=gemini node scripts/benchmark-thinking.js",

59 "refresh-models": "node bin/amicus.js models --refresh",

60 "models:info": "node bin/amicus.js models",

61 "models:check": "node bin/amicus.js models --check",

62 "generate-icon": "node scripts/generate-icon.js",

63 "generate-docs": "node scripts/generate-docs.js",

64 "generate-docs:check": "node scripts/generate-docs.js --check",

65 "validate-docs": "node scripts/validate-docs.js --full",

66 "setup-hooks": "node scripts/setup-hooks.js",

67 "check:secrets": "node scripts/check-secrets.js --all",

68 "check:sizes": "node scripts/check-file-sizes.js --all",

69 "check:tarball": "node scripts/check-tarball-lifecycle.js"

70 },

71 "dependencies": {

72 "@modelcontextprotocol/sdk": "^1.27.0",

73 "@opencode-ai/sdk": "^1.1.36",

74 "dotenv": "^17.2.3",

75 "opencode-ai": "^1.2.20",

76 "tiktoken": "^1.0.0",

bin/amicus.jsView file

Lines 1-33javascript

1#!/usr/bin/env node

3/**

4 * Amicus CLI Entry Point

5 *

6 * Spec Reference: §4 CLI Interface

7 * Routes commands to appropriate handlers.

8 */

10// One-time, non-destructive migration of the legacy ~/.config/sidecar dir onto

11// the canonical ~/.config/amicus (copy; legacy kept as a backup). Runs before

12// any config/credential read so both resolve to the unified dir. Best-effort.

13try {

14 const { migrateLegacyConfigDir } = require('../src/utils/config');

15 const _m = migrateLegacyConfigDir();

Medium

Dynamic Require

Package source references dynamic require/import behavior.

bin/amicus.jsView on unpkg · L13

16 if (_m && _m.migrated) {

17 process.stderr.write(`[amicus] Migrated config ${_m.from} → ${_m.to} (legacy kept as a backup).\n`);

18 }

19} catch { /* best-effort: never block startup on migration */ }

21// Load API keys from all sources: process.env > sidecar .env > auth.json

22const { loadCredentials } = require('../src/utils/env-loader');

23loadCredentials();

25const { parseArgs, getUsage } = require('../src/cli');

26const { validateTaskId } = require('../src/utils/validators');

27const { resolveModelFromArgs, validateFallbackModel } = require('../src/utils/start-helpers');

28const { handleSetup, handleAbort, handleUpdate, handleMcp, handleKey } = require('../src/cli-handlers');

29const { handleStart, handleFanout, handleRead } = require('../src/cli-handlers-run');

30const { isOneShotCommand, armExitWatchdog } = require('../src/utils/lifecycle');

31const { logger } = require('../src/utils/logger');

33const VERSION = require('../package.json').version;

scripts/postinstall.jsView file

Lines 1-25javascript

1#!/usr/bin/env node

3/**

4 * Post-install script for amicus

5 *

6 * 1. Copies SKILL.md to ~/.claude/skills/sidecar/

7 * 2. Registers MCP server in Claude Code (~/.claude.json)

8 * 3. Registers MCP server in Claude Desktop/Cowork config

9 */

11const fs = require('fs');

12const path = require('path');

13const os = require('os');

Critical

Ai Agent Control Hijack

Install-time source drops package-supplied AI-agent/MCP control files or instructions.

scripts/postinstall.jsView on unpkg · L5

14const { execFileSync } = require('child_process');

16const { repairElectron } = require('../src/sidecar/electron-install');

17const HINTS = require('../src/utils/remediation-hints');

19const SETUP_HOOKS_SCRIPT = path.join(__dirname, 'setup-hooks.js');

21/** Short cache-only provision budget: a slow disk must never hang the install. */

22const PROVISION_TIMEOUT_MS = 15000;

24const SKILL_SOURCE = path.join(__dirname, '..', 'skills', 'sidecar', 'SKILL.md');

25const COUNCIL_SOURCE_DIR = path.join(__dirname, '..', 'skills', 'second-opinion');

src/sidecar/electron-install.jsView file

Critical

Previous Version Dangerous Delta

This package version adds a dangerous source file absent from the previous stored version.

src/sidecar/electron-install.jsView on unpkg