nanoid: Integer Overflow or Wraparound

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

nanoid is a secure, URL-friendly, unique string ID generator for JavaScript. Prior to versions 3.3.12 and 5.1.11, the nanoid(size) function in index.js and index.cjs coerces the user-influenced size parameter to a signed 32-bit integer, allowing a value of 2147483648 to become -2147483648 and corrupt the process-wide CSPRNG poolOffset in fillPool(), which causes subsequent session tokens, CSRF tokens, API keys, and unique identifiers to become the deterministic string "uuuuuuuuuuuuuuuuuuuuu" until the process restarts. This issue is fixed in versions 3.3.12 and 5.1.11.

Source published

11 Aug 2026 16:46:23 UTC

Source modified

12 Aug 2026 14:29:36 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

nanoid is a secure, URL-friendly, unique string ID generator for JavaScript. Prior to versions 3.3.12 and 5.1.11, the nanoid(size) function in index.js and index.cjs coerces the user-influenced size parameter to a signed 32-bit integer, allowing a value of 2147483648 to become -2147483648 and corrupt the process-wide CSPRNG poolOffset in fillPool(), which causes subsequent session tokens, CSRF tokens, API keys, and unique identifiers to become the deterministic string "uuuuuuuuuuuuuuuuuuuuu" until the process restarts. This issue is fixed in versions 3.3.12 and 5.1.11.

Source published

11 Aug 2026 17:19:16 UTC

Source modified

24 Oct 2026 15:10:00 UTC

Observed here

25 Oct 2026 15:19:03 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

### 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 published

1 Sep 2026 19:23:45 UTC

Source modified

1 Sep 2026 19:30:08 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Publisher rating · HIGH