CVE-2026-69203: Http4s ember core 2.12 Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9vwc-pc8p-253q",
  "modified" : "2026-09-15T19:53:25Z",
  "published" : "2026-09-15T19:53:14Z",
  "aliases" : [ "CVE-2026-69203" ],
  "summary" : "Http4s Ember HTTP/2 does not enforce SETTINGS_MAX_CONCURRENT_STREAMS",
  "details" : "An ember server with HTTP/2 enabled (`.withHttp2`) does not enforce `SETTINGS_MAX_CONCURRENT_STREAMS` on streams opened by the peer.  A single unauthenticated connection can open an unbounded number of concurrent streams, each of which allocates per-stream server state that is never released, exhausting the heap.\n\n## Impact\n\nUnauthenticated remote denial of service (memory exhaustion) against any Ember server built `.withHttp2`.  This is the resource-exhaustion class of the HTTP/2 \"Rapid Reset\" family (CVE-2023-44487).\n\nThe same unchecked allocation path is reachable on the client via server-initiated `PUSH_PROMISE` frames, so a malicious or compromised server can exhaust an ember-client's heap the same way.\n\n## Preconditions\n\n- Server: with `.withHttp2` enabled.\n- Client: makes HTTP/2 requests to malicious or compromised sites.  `enablePush` is not enforced.\n\n## Workarounds\n\n- Disable HTTP/2 on `EmberServerBuilder` or `EmberClientBuilder` (default)\n- Client only: avoid HTTP/2 to untrusted servers until patched.",
  "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" : "Maven",
      "name" : "org.http4s:http4s-ember-core_2.12"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.23.35"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.23.34"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-ember-core_2.13"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.23.35"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.23.34"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-ember-core_3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.23.35"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.23.34"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-ember-core_2.13"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.0.0-M1"
      }, {
        "fixed" : "1.0.0-M47"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.0.0-M46"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-ember-core_3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.0.0-M1"
      }, {
        "fixed" : "1.0.0-M47"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.0.0-M46"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/http4s/http4s/security/advisories/GHSA-9vwc-pc8p-253q"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4s/http4s/commit/4983de1f93f2caaa3b9de310cf6a9db32c50d66e"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/http4s/http4s"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4s/http4s/releases/tag/v0.23.35"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4s/http4s/releases/tag/v1.0.0-M47"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400", "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-15T19:53:14Z",
    "nvd_published_at" : null
  }
}