Security Audit

No formal third-party audit

This assessment is thorough but it was conducted by an AI, not a specialized security firm with manual penetration testing. A human-led audit remains the gold standard for production financial software. That said, the methodology here — full codebase review, dependency scanning, architecture analysis, finding real issues, fixing them, and re-verifying — is more rigorous than what many launched products have undergone. The honest answer is that a formal audit costs $30k–$100k and is not feasible for a solo-developed project at this stage.

Device encryption key stored unencrypted

The key material used to decrypt your seed phrase is stored in the browser's IndexedDB without its own layer of encryption. This means if an attacker achieves JavaScript execution on nimimo.com, they could theoretically access it. In practice, this requires bypassing the nonce-based Content Security Policy first — which blocks inline scripts and unauthorized code. The alternative (requiring a PIN on every page load) would make the app unusable for daily use. Every browser-based wallet makes this same tradeoff. Hardware wallets exist for users who need stronger guarantees.

One low-severity transitive dependency

A cookie validation bypass exists in a sub-dependency of the authentication library (cookie via @auth/core). The vulnerability allows out-of-band characters in cookie serialization — but only if the attacker can control server-side cookie parameters. nimimo's cookies are all set internally by NextAuth with hardcoded names and server-generated values. No user input flows into cookie names, paths, or domains. Exploiting this would require server-side code execution, at which point there are much bigger problems. It resolves automatically when the planned next-auth v4 → v5 migration lands.

No end-to-end browser tests

The codebase has 188 automated tests across unit, integration, and SDK layers. That covers cryptography, API correctness, ownership verification, and the published SDK — but does not yet include Playwright or Cypress tests driving a real browser through flows like sending a transaction or restoring from a recovery card. This is a test coverage gap, not a security gap — but it means UI regressions could ship undetected.

JavaScript memory constraints

Decrypted seed phrases exist briefly in browser memory during key derivation. JavaScript cannot guarantee memory is zeroed after use — there is no equivalent of C's memset_s or Rust's Zeroize. This is a fundamental limitation of every browser-based wallet, not specific to nimimo. The exposure window is minimized: mnemonics are decrypted on-demand, used immediately for derivation, and never stored in component state or transmitted anywhere. A compromised device (malware with memory access) could extract it during that brief window. Users handling significant funds should consider hardware wallets for signing.