GCVE Workshop - 22 September 2026 (14:00-18:00), Luxembourg Before The Vulnopticon Conference - Registration

GHSA-8H4C-X2WG-6XP8

Vulnerability from github – Published: 2026-09-15 19:53 – Updated: 2026-09-15 19:53
VLAI
Summary
Http4s Ember accepts Transfer-Encoding combined with Content-Length (CL.TE request smuggling)
Details

Summary

Ember's HTTP/1.1 request parser does not reject a message that carries both a Transfer-Encoding and a Content-Length header. RFC 9112 §6.1 requires a server to treat such a message as a framing error and close the connection. An intermediary that follows the RFC's CL-strip-and-forward path (or that prioritises Content-Length) will frame the body differently from Ember, enabling HTTP request smuggling (CL.TE).

Impact

Server

Request smuggling when ember-server is an origin behind an intermediary that forwards both headers over a keep-alive backend connection and frames by Content-Length while Ember frames by chunked:

  • Front-end security bypass: the smuggled request reaches paths the intermediary's ACL/auth layer would have blocked, with attacker-chosen method and headers.
  • Cross-user request hijack: a dangling smuggled prefix concatenates with the next victim's request on the shared backend socket, capturing its headers.
  • Cache poisoning: the smuggled response is associated with the next request key in a caching proxy.

Client

ember-client shares the same parser on the response path. An upstream that sends both headers can desync a pooled client connection. This requires a malicious or compromised upstream.

Preconditions

  • Unauthenticated remote attacker (server)
  • ember-server as origin behind a keep-alive intermediary
  • Intermediary forwards a request carrying both Transfer-Encoding and Content-Length (RFC says it MAY reject; many forward) and frames by Content-Length
  • Malicious or compromised upstream (client)

Workarounds

  • Intermediary strictly rejects requests carrying both Transfer-Encoding and Content-Length
  • Intermediary buffers and re-encodes request bodies
  • Disable backend keep-alive between the intermediary and Ember
Severity
9.2 (Critical)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.23.34"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4s:http4s-ember-core_2.12"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.23.35"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.23.34"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4s:http4s-ember-core_2.13"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.23.35"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.23.34"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4s:http4s-ember-core_3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.23.35"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.0.0-M46"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4s:http4s-ember-core_2.13"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.0.0-M1"
            },
            {
              "fixed": "1.0.0-M47"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.0.0-M46"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4s:http4s-ember-core_3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.0.0-M1"
            },
            {
              "fixed": "1.0.0-M47"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-69204"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-444"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-15T19:53:44Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "## Summary\n\nEmber\u0027s HTTP/1.1 request parser does not reject a message that carries both a\n`Transfer-Encoding` and a `Content-Length` header. RFC 9112 \u00a76.1 requires a\nserver to treat such a message as a framing error and close the connection.\nAn intermediary that follows the RFC\u0027s CL-strip-and-forward path (or that\nprioritises `Content-Length`) will frame the body differently from Ember,\nenabling HTTP request smuggling (CL.TE).\n\n## Impact\n\n### Server\n\nRequest smuggling when ember-server is an origin behind an intermediary that\nforwards both headers over a keep-alive backend connection and frames by\n`Content-Length` while Ember frames by chunked:\n\n- Front-end security bypass: the smuggled request reaches paths the\n  intermediary\u0027s ACL/auth layer would have blocked, with attacker-chosen\n  method and headers.\n- Cross-user request hijack: a dangling smuggled prefix concatenates with the\n  next victim\u0027s request on the shared backend socket, capturing its headers.\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 parser on the response path. An upstream that\nsends both headers can desync a pooled client connection. This requires a\nmalicious or compromised upstream.\n\n## Preconditions\n\n- Unauthenticated remote attacker (server)\n- ember-server as origin behind a keep-alive intermediary\n- Intermediary forwards a request carrying both `Transfer-Encoding` and\n  `Content-Length` (RFC says it MAY reject; many forward) and frames by\n  `Content-Length`\n- Malicious or compromised upstream (client)\n\n## Workarounds\n\n- Intermediary strictly rejects requests carrying both `Transfer-Encoding`\n  and `Content-Length`\n- Intermediary buffers and re-encodes request bodies\n- Disable backend keep-alive between the intermediary and Ember",
  "id": "GHSA-8h4c-x2wg-6xp8",
  "modified": "2026-09-15T19:53:44Z",
  "published": "2026-09-15T19:53:44Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/http4s/http4s/security/advisories/GHSA-8h4c-x2wg-6xp8"
    },
    {
      "type": "WEB",
      "url": "https://github.com/http4s/http4s/commit/9feaf8677951a52af906ae9664ff6f0543d9d810"
    },
    {
      "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Http4s Ember accepts Transfer-Encoding combined with Content-Length (CL.TE request smuggling)"
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.