GHSA-xwg4-73v4-xw9w nanoid: Integer Overflow or Wraparound

• npm nanoid: < 3.3.12 → fixed in 3.3.12 • npm nanoid: >= 4.0.0, < 5.1.11 → fixed in 5.1.11

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` 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`): ```javascript function fillPool(bytes) { if (!pool || pool.length 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