CVE-2026-63462: Unleash Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-r5pq-6chh-j3xp",
  "modified" : "2026-08-21T19:14:37Z",
  "published" : "2026-08-21T19:14:37Z",
  "aliases" : [ "CVE-2026-63462" ],
  "summary" : "Unleash: Unauthenticated single-request DoS via OpenAPI validation error formatter",
  "details" : "## Summary\n\nAn unauthenticated `POST` to any OpenAPI-validated endpoint, including the anonymous `POST /edge/validate` and `POST /edge/issue-token`, crashes the entire Unleash server with one request body of deeply-nested JSON.\n\nWhen request-body validation fails, Unleash builds the error message by calling `JSON.stringify` on the raw offending value taken from the request body. A value nested a few thousand levels deep makes `JSON.stringify` recurse past the V8 call-stack limit and throw `RangeError: Maximum call stack size exceeded`.\n\nThe throw is synchronous inside an Express error-handling middleware that has no try/catch, and the process registers no `uncaughtException` handler (only `unhandledRejection`). Node terminates the process with `exit(1)`.\n\nThe body parser sets no JSON nesting-depth limit, the payload (about 10 KB at depth 5000) stays far under the 100 KB body-size limit, and the same error formatter serves every API route, so the trigger is route-independent.\n\nResult: a remote attacker with no account, token, or cookie takes the whole server offline with a single 10 KB request, and keeps it offline by replaying it.\n\n## Affected\n\nUnleash OSS server, confirmed live-exploitable on v8.0.0 (`unleashorg/unleash-server:8.0.0`).\nVulnerable code is the shared request-validation error path (`src/lib/error/bad-data-error.ts` `genericErrorMessage`), present on current `main`.\nReachable on a stock install: no feature flag, no setting, no authentication, no CSRF token, and no cookie required.\nThe 100 KB request-body size limit does not mitigate it; the crashing payload is about 10 KB.\n\n## Root cause\n\nOn validation failure the error formatter serializes the raw offending request value with an unguarded `const youSent = JSON.stringify(propertyValue)` (`src/lib/error/bad-data-error.ts:75`), where `propertyValue` is read straight from the request body via `lodash.get` (`bad-data-error.ts:123`). A deeply-nested array or object makes `JSON.stringify` recurse once per level and throw `RangeError: Maximum call stack size exceeded`. `fromOpenApiValidationErrors` (`bad-data-error.ts:158`) runs from the Express error middleware `openAPIValidationMiddleware` (`src/lib/routes/controller.ts:68`), which calls it with no try/catch (`controller.ts:70`), while the controller's own try/catch (`controller.ts:103`) wraps only the route handler. The process registers only `process.on('unhandledRejection')` (`src/lib/server-impl.ts:274`) and no `uncaughtException` handler, so the synchronous throw terminates Node with `exit(1)`. The same unguarded pattern exists at `fromJoiError` (`bad-data-error.ts:175`) and at `handleErrors` (`src/lib/routes/util.ts:42`), whose own comment records that `JSON.stringify(finalError.details)` \"also hangs\" (`util.ts:63`).\n\n## Reproduction\n\n`unleashorg/unleash-server:8.0.0` started from the repository `docker-compose.yml`, default config, no credentials, server at `http://localhost:4242`.\n\n1. A shallow body returns a normal 400 and the server stays up.\n\n```\ncurl -s -X POST http://localhost:4242/edge/validate \\\n  -H 'Content-Type: application/json' -d '{\"tokens\":[[]]}'\n# HTTP 400 BadDataError: \"The `/body/tokens/0` property must be string. You sent [].\"\n```\n\n2. A single anonymous body nested 5000 levels deep (10013 bytes) crashes the process.\n\n```\ncurl -s -o /dev/null -w '%{http_code}\\n' -X POST http://localhost:4242/edge/validate \\\n  -H 'Content-Type: application/json' \\\n  --data-binary \"$(python3 -c 'd=5000;print(\"{\\\"tokens\\\":[\"+\"[\"*d+\"]\"*d+\"]}\")')\"\n# 000  (connection dropped mid-response; Node exited)\n```\n\n3. The server is gone and does not recover on its own.\n\n```\ncurl -s -o /dev/null -w '%{http_code}\\n' http://localhost:4242/health\n# 000\ndocker inspect repo-web-1 --format '{{.State.Status}} restarts={{.RestartCount}}'\n# exited restarts=0\n```\n\nLive-verified: one anonymous 10013-byte request to `/edge/validate` drove `/health` from 200 to 000; the container logs showed the `RangeError` stack through `bad-data-error` and `openAPIValidationMiddleware`, and the process did not restart. The crash threshold is about 4000 to 4500 nesting levels; depth 5000 crashes reliably. The same crash reproduces on `POST /edge/issue-token` with a nested object, confirming route and shape independence.\n\n## Impact\n\n- Single 10 KB request with no account, token, or cookie takes the entire server offline.\n- Replaying the request (kilobits per restart interval) sustains a near-total outage; with no restart policy the first request is a permanent kill.\n- Feature-flag evaluation sits on the request path of dependent applications, so the outage propagates to them.\n- Every OpenAPI-validated endpoint is a trigger, including anonymous ones.\n\n## Credit\n\nJan Kahmen, [turingpoint](https://www.turingpoint.de) (jan@turingpoint.de)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "unleash-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.5.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "unleash-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "7.6.0"
      }, {
        "fixed" : "7.6.5"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "unleash-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "8.0.0"
      }, {
        "fixed" : "8.0.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/Unleash/unleash/security/advisories/GHSA-r5pq-6chh-j3xp"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Unleash/unleash/commit/b0e4da63249a9403bc209e0581db223326cb8dcf"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Unleash/unleash/commit/d45f99df924c0d24747b3e45e46fcda7dcd3c1c1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Unleash/unleash/commit/d862562a5ab8f2d1e40f6519c64cf0b4fdaf806d"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/Unleash/unleash"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Unleash/unleash/releases/tag/v7.5.2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Unleash/unleash/releases/tag/v7.6.5"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Unleash/unleash/releases/tag/v8.0.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-674" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-21T19:14:37Z",
    "nvd_published_at" : null
  }
}