CVE-2026-100409: OpenNext Cloudflare Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2vc4-c4r6-p6v6",
  "modified" : "2026-10-15T20:15:17Z",
  "published" : "2026-10-15T20:15:17Z",
  "aliases" : [ "CVE-2026-100409" ],
  "summary" : "OpenNext Cloudflare: Cache interception can bypass middleware protection for encoded paths",
  "details" : "## Summary\n\nWhen cache interception is enabled, `@opennextjs/cloudflare` can interpret percent-encoded paths differently during middleware matching and cache lookup.\n\nAn encoded request may fail to match authorization middleware, then be decoded into the cache key of a protected route. The cached response may consequently be returned without invoking the middleware.\n\n`enableCacheInterception` is disabled by default.\n\n## Impact\n\nA remote unauthenticated attacker may retrieve cached content from routes intended to be protected by middleware.\n\nAn application is affected when it:\n\n- explicitly enables `enableCacheInterception`;\n- relies on middleware for access control; and\n- has a matching cached route.\n\n## Details\n\nMiddleware matching previously used the encoded request pathname, while cache interception decoded the pathname before selecting a cache entry.\n\nFor example, consider an application with:\n\n- middleware matcher `/admin/:path*`;\n- middleware returning `401 Authentication required` for `/admin`;\n- a statically generated, cached `/admin` route; and\n- cache interception enabled:\n\n```ts\nexport default defineCloudflareConfig({\n  incrementalCache: staticAssetsIncrementalCache,\n  enableCacheInterception: true,\n});\n```\n\nAn attacker can request:\n\n```http\nGET /%61dmin\n```\n\nThe encoded pathname does not match `/admin/:path*`, so the authorization middleware is not invoked. Cache interception then decodes `%61dmin` to `admin` and may return the cached `/admin` response:\n\n```http\nHTTP/1.1 200 OK\nx-opennext-cache: HIT\n\nProtected content\n```\n\nMalformed paths exposed an additional inconsistency. For example:\n\n```http\nGET /%61dmin/%ZZ\n```\n\nThe previous implementation decoded each segment independently. It decoded `%61dmin` to `admin` but retained the malformed `%ZZ` segment, allowing cache lookup to continue using a partially decoded pathname.\n\n## Patches\n\nThe fix aligns encoded-path handling across middleware matching and cache lookup, and rejects malformed paths instead of partially decoding them. See the upstream fixes in [opennextjs-aws#1199](https://github.com/opennextjs/opennextjs-aws/pull/1199) and [opennextjs-aws#1200](https://github.com/opennextjs/opennextjs-aws/pull/1200).\n\nUsers should upgrade to `@opennextjs/cloudflare@1.20.2` or later.\n\n## Workarounds\n\nIf upgrading is not immediately possible for an application:\n\n1. Disable cache interception by removing `enableCacheInterception: true`.\n2. Enforce authorization inside protected route handlers rather than relying exclusively on middleware.\n3. Reject encoded paths for protected routes at a trusted proxy before they reach the Worker.\n\nAdding individual encoded matcher variants is not a complete workaround because pathnames can have multiple equivalent encodings.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@opennextjs/cloudflare"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.3.0"
      }, {
        "fixed" : "1.20.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/opennextjs/opennextjs-cloudflare/security/advisories/GHSA-2vc4-c4r6-p6v6"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-100409"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/opennextjs/opennextjs-aws/pull/1199"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/opennextjs/opennextjs-aws/pull/1200"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/opennextjs/opennextjs-cloudflare/commit/38ea40b669be272ddf09a7df7e70c69d0b57404b"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/opennextjs/opennextjs-cloudflare"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/opennextjs/opennextjs-cloudflare/releases/tag/@opennextjs/cloudflare@1.20.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-177", "CWE-180" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-15T20:15:17Z",
    "nvd_published_at" : "2026-10-15T17:17:07Z"
  }
}