CVE-2026-69205: Http4s ember core 3 Http4s Ember Transfer-Encoding Value Parsing Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9998-894r-fwvr",
  "modified" : "2026-09-15T19:54:25Z",
  "published" : "2026-09-15T19:54:25Z",
  "aliases" : [ "CVE-2026-69205" ],
  "summary" : "Http4s Ember Transfer-Encoding value parsing (TE.CL / TE.0 request smuggling)",
  "details" : "## Summary\n\nEmber's HTTP/1.1 header parser matches the `Transfer-Encoding` header value\nwith a case-sensitive substring test (`hValue.contains(\"chunked\")`). RFC\n9112 §7 requires transfer-coding names to be compared case-insensitively. A\nrequest carrying `Transfer-Encoding: Chunked` (capital C) is therefore not\nrecognised as chunked, and Ember falls back to framing by `Content-Length`\n(or zero if absent) while a compliant intermediary frames the same bytes by\nchunked encoding. The two parsers then disagree on where the request body\nends, enabling HTTP request smuggling (TE.CL / TE.0).\n\nThe same line of code admits two further variants:\n\n- The substring test misfires on `Transfer-Encoding: notchunked` (an inverse\n  desync — Ember treats it as chunked while a compliant intermediary\n  rejects the unknown coding).\n- Header field bytes are decoded with the platform-default charset. Under\n  UTF-8 the wire bytes `E2 84 AA` decode to U+212A KELVIN SIGN, which\n  `String.equalsIgnoreCase` Unicode-case-folds to `k`, so\n  `Transfer-Encoding: chun<U+212A>ed` matches `chunked` once the comparison\n  is made case-insensitive without also pinning the decode to ISO-8859-1.\n\n## Impact\n\n### Server\n\nRequest smuggling when ember-server is an origin behind an intermediary that\nhonours `Transfer-Encoding` case-insensitively per RFC, forwards the header\nvalue verbatim, and reuses keep-alive connections to the backend:\n\n- Front-end security bypass: the smuggled request reaches paths the\n  intermediary's ACL/auth layer would have blocked, with attacker-chosen\n  method and headers.\n- Cross-user request hijack: a partial smuggled prefix left in Ember's\n  connection buffer is concatenated with the next victim's request on the\n  same pooled backend connection, exposing its headers (e.g. `Cookie`,\n  `Authorization`) to the attacker.\n- Cache poisoning: the smuggled response is associated with the next request\n  key in a caching proxy.\n\n### Client\n\nember-client shares the same `HeaderP.parse` on the response path, enabling\nresponse smuggling when http4s is used as a gateway. This is less severe: it\nrequires a malicious or compromised upstream rather than an anonymous remote\nclient.\n\n## Preconditions\n\n- Unauthenticated remote attacker (server)\n- ember-server as origin behind a keep-alive intermediary\n- Intermediary treats `Transfer-Encoding` case-insensitively (per RFC) and\n  forwards the header value without lowercasing it\n- Malicious or compromised upstream (client)\n\n## Workarounds\n\n- Intermediary fully buffers and re-encodes request bodies (e.g. nginx with\n  default `proxy_request_buffering on`)\n- Intermediary normalises the `Transfer-Encoding` value (lowercases the\n  token) before forwarding\n- Disable backend keep-alive between the intermediary and Ember",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "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" : "0"
      }, {
        "fixed" : "0.23.35"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.23.34"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-ember-core_2.12"
    },
    "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" : "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-9998-894r-fwvr"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4s/http4s/commit/5e88b2e7b4e6ea2f0c61040a4bc9de0d73e51217"
  }, {
    "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-444" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-15T19:54:25Z",
    "nvd_published_at" : null
  }
}