CVE-2026-69202: Http4s Ember HTTP/2 Unbounded Inbound Body Buffering Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-6m4x-pp6q-5jmm",
  "modified" : "2026-09-15T19:52:58Z",
  "published" : "2026-09-15T19:52:58Z",
  "aliases" : [ "CVE-2026-69202" ],
  "summary" : "Http4s Ember HTTP/2: unbounded inbound body buffering",
  "details" : "Ember's HTTP/2 stack replenishes the inbound flow-control window based on bytes\nreceived off the wire, not bytes consumed by the application.  Received DATA is buffered in an unbounded per-stream channel.  Flow control therefore\nprovides no backpressure: a peer can stream a large or unbounded body faster than the application drains it and the connection retains every payload in heap.\n\nThis is the read-path mirror of the [outbound queue issue](https://github.com/http4s/http4s/security/advisories/GHSA-8f3q-3jmv-7prw).\n\nThis affects an Ember receiving a request body and an Ember client receiving a response body from a hostile server.\n\n### Impact\n\nUnauthenticated remote denial of service (OOM) against any Ember server built\n`.withHttp2` for a non-draining or slow-draining route, and against an Ember client consuming from a hostile or compromised server.\n\n### Workarounds\n\n- Disable HTTP/2 to remove the vector entirely.\n- Apply an aggregate request-entity size limit (e.g. `EntityLimiter` middleware) on routes that consume the body.\n- Ensure handlers fully drain request bodies with aggressive idle timeouts.",
  "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-6m4x-pp6q-5jmm"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4s/http4s/commit/22d2335975d02dc9fb9fb75cfe002279521d86ac"
  }, {
    "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" : "2026-09-15T19:52:58Z",
    "nvd_published_at" : null
  }
}