CVE-2026-73086

nanoid: Integer Overflow or Wraparound

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
}

for (let i = poolOffset - size; i < poolOffset; i++) {
  id += scopedUrlAlphabet[pool[i] & 63]
}

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

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

An arithmetic operation produces a value that exceeds the integer type's maximum, causing it to wrap to an unexpected small value. Typical impact: incorrect size calculations leading to heap overflows or logic errors.

CVE-2026-73086 has a CVSS score of 7.4 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.3.12, 5.1.11); upgrading removes the vulnerable code path.

Kodem intelligence

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1. What is CVE-2026-73086? CVE-2026-73086 is a high-severity integer overflow or wraparound vulnerability in nanoid (npm), affecting versions < 3.3.12. It is fixed in 3.3.12, 5.1.11. An arithmetic operation produces a value that exceeds the integer type's maximum, causing it to wrap to an unexpected small value.
2. How severe is CVE-2026-73086? CVE-2026-73086 has a CVSS score of 7.4 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of nanoid are affected by CVE-2026-73086? nanoid (npm) versions < 3.3.12 is affected.
4. Is there a fix for CVE-2026-73086? Yes. CVE-2026-73086 is fixed in 3.3.12, 5.1.11. Upgrade to this version or later.
5. Is CVE-2026-73086 exploitable, and should I be worried? Whether CVE-2026-73086 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-73086 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-73086?
   • Upgrade nanoid to 3.3.12 or later
   • Upgrade nanoid to 5.1.11 or later

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