nanoid: Integer Overflow or Wraparound

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-73086: 0.30% estimated exploitation activity in the next 30 days; percentile 22.38 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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): Neither branch triggers, so the pool is never refreshed. poolOffset becomes ~-2.1 billion. Subsequent nanoid() calls execute: pool[negativeindex] 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…

Published by the source

1 Sep 2026, 19:23 UTC

Last modified by the source

1 Sep 2026, 19:23 UTC

Source last checked

26 Oct 2026, 13:02 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-xwg4-73v4-xw9w

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# Patch Next advisory brief: CVE-2026-73086

Advisory: nanoid: Integer Overflow or Wraparound
IDs: CVE-2026-73086, GHSA-xwg4-73v4-xw9w
Record: https://patchnext.com/advisories/cve-2026-73086 (revision 1, source checked 26 Oct 2026, 13:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nanoid 5.1.11, 3.3.12. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm nanoid: affected < 3.3.12; >= 4.0.0, < 5.1.11; fixed in 3.3.12, 5.1.11

## Suggested inspection (read-only)
- `npm ls nanoid --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nanoid.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-xwg4-73v4-xw9w (GitHub-reviewed advisory GHSA-xwg4-73v4-xw9w lists affected ranges: npm nanoid >=0 =4.0.0 <5.1.11)

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