CVE-2026-73493: blaze Unbounded WebSocket Message Aggregation Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-7ppr-r889-mcf2",
  "modified" : "2026-08-12T21:08:44Z",
  "published" : "2026-07-24T22:28:05Z",
  "aliases" : [ "CVE-2026-73493" ],
  "summary" : "blaze: Unbounded WebSocket message aggregation in http4s-blaze-server",
  "details" : "## Summary\n\n`http4s-blaze-server` aggregates the fragments of an incoming WebSocket\nmessage with no limit on total size or fragment count. A client that\ncompletes a WebSocket handshake can send an unterminated fragmented\nmessage and drive unbounded heap growth in the server JVM, resulting in\ndenial of service via `OutOfMemoryError`.\n\n## Impact\n\nAny http4s application serving WebSocket routes over\n`BlazeServerBuilder` is affected; no non-default configuration is required,\nand `maxWebSocketBufferSize` does not bound the aggregate (it bounds only\nindividual frames). A single connection sending continuation frames that\nnever set FIN forces the server to buffer every fragment until the heap is\nexhausted, terminating the JVM with `OutOfMemoryError` on the blaze\nselector thread. Small fragments amplify the cost through per-frame object\noverhead, so a modest volume of wire bytes is sufficient. Where the\nWebSocket endpoint is reachable without authentication the attacker is\nunauthenticated and remote; where the handshake requires a principal, any\nauthenticated client can still trigger it.\n\n## Workarounds\n\n- No blaze-server configuration bounds the aggregate; `maxWebSocketBufferSize`\n  is not a mitigation.\n- Terminate/limit WebSocket traffic at a fronting layer that enforces\n  message-size and fragment limits, or disable WebSocket routes.\n- Longer term: blaze is EOL upstream; plan migration to a maintained\n  backend (e.g. ember).",
  "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-blaze-server_2.13"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.23.18"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-blaze-server_2.13"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.0.0-M1"
      }, {
        "fixed" : "1.0.0-M42"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-blaze-server_2.12"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.23.18"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-blaze-server_3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.0.0-M1"
      }, {
        "fixed" : "1.0.0-M42"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/http4s/blaze/security/advisories/GHSA-7ppr-r889-mcf2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4s/blaze/commit/173e8ca820a0d12110bfe409c72e9b9c3d28d471"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4s/blaze/commit/2ae13a74d55209b6573d5228d1aa94f0361a75d0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4s/blaze/commit/fadbe6d0f7f59045425688d313c8d4804973d12f"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/http4s/blaze"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4s/blaze/releases/tag/v0.23.18"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4s/blaze/releases/tag/v1.0.0-M42"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-24T22:28:05Z",
    "nvd_published_at" : null
  }
}