CVE-2021-41084: Http4s client 2.12 Response Splitting From Unsanitized Headers Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5vcm-3xc3-w7x3",
  "modified" : "2025-12-11T21:12:05Z",
  "published" : "2021-09-22T19:18:41Z",
  "aliases" : [ "CVE-2021-41084" ],
  "summary" : "Response Splitting from unsanitized headers",
  "details" : "### Impact\n\nhttp4s is vulnerable to response-splitting or request-splitting attacks when untrusted user input is used to create any of the following fields:\n\n* Header names (`Header.name`å\n* Header values (`Header.value`)\n* Status reason phrases (`Status.reason`)\n* URI paths (`Uri.Path`)\n* URI authority registered names (`URI.RegName`) (through 0.21)\n\nThe following backends render invalid carriage return, newline, or null characters in an unsafe fashion.\n\n|                | blaze-server | ember-server | blaze-client | ember-client | jetty-client |\n|:---------------|:-------------|:-------------|:-------------|--------------|--------------|\n| header names   | ⚠            | ⚠            | ⚠            | ⚠            |   ⚠            | \n| header values  | ⚠            | ⚠            | ⚠            | ⚠            |              |\n| status reasons | ⚠            | ⚠            |              |              |              |\n| URI paths      |              |              |  ⚠             |  ⚠             |              |\n| URI regnames   |              |              |  ⚠ < 0.22           |  ⚠ < 0.22            |              |\n\nFor example, given the following service:\n\n```scala\nimport cats.effect._\nimport org.http4s._\nimport org.http4s.dsl.io._\nimport org.http4s.server.blaze.BlazeServerBuilder\nimport scala.concurrent.ExecutionContext.global\n\nobject ResponseSplit extends IOApp {\n  override def run(args: List[String]): IO[ExitCode] =\n    BlazeServerBuilder[IO](global)\n      .bindHttp(8080)\n      .withHttpApp(httpApp)\n      .resource\n      .use(_ => IO.never)\n\n  val httpApp: HttpApp[IO] =\n    HttpApp[IO] { req =>\n      req.params.get(\"author\") match {\n        case Some(author) =>\n          Ok(\"The real content\")\n            .map(_.putHeaders(Header(\"Set-Cookie\", s\"author=${author}\")))\n        case None =>\n          BadRequest(\"No author parameter\")\n      }\n    }\n}\n```\n\nA clean `author` parameter returns a clean response:\n\n```sh\ncurl -i 'http://localhost:8080/?author=Ross'\n```\n\n```http\nHTTP/1.1 200 OK\nContent-Type: text/plain; charset=UTF-8\nSet-Cookie: author=Ross\nDate: Mon, 20 Sep 2021 04:12:10 GMT\nContent-Length: 16\n\nThe real content\n```\n\nA malicious `author` parameter allows a user-agent to hijack the response from our server and return different content:\n\n```sh\ncurl -i 'http://localhost:8080/?author=hax0r%0d%0aContent-Length:+13%0d%0a%0aI+hacked+you'\n```\n\n```http\nHTTP/1.1 200 OK\nContent-Type: text/plain; charset=UTF-8\nSet-Cookie: author=hax0r\nContent-Length: 13\n\nI hacked you\n```\n\n### Patches\n\nVersions 0.21.29, 0.22.5, 0.23.4, and 1.0.0-M27 perform the following:\n\n* If a status reasoon phrase is invalid, it is dropped. Rendering is optional per spec.\n* If a header name is invalid in a request or response, the header is dropped.  There is no way to generically sanitize a header without potentially shadowing a correct one.\n* If a header value is invalid in a request or response, it is sanitized by replacing null (`\\u0000`), carriage return (`\\r`), and newline (`\\n`) with space (` `) characters per spec.\n* If a URI path or registered name is invalid in a request line, the client raises an `IllegalArgumentException`.\n* If a URI registered name is invalid in a host header, the client raises an `IllegalArgumentException`. \n\n### Workarounds\n\nhttp4s services and client applications should sanitize any user input in the aforementioned fields before returning a request or response to the backend.  The carriage return, newline, and null characters are the most threatening.\n\nNot all backends were affected: jetty-server, tomcat-server, armeria, and netty on the server; async-http-client, okhttp-client, armeria, and netty as clients.\n\n### References\n* https://owasp.org/www-community/attacks/HTTP_Response_Splitting\n* https://httpwg.org/http-core/draft-ietf-httpbis-semantics-latest.html#fields.values\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [GitHub](http://github.com/http4s/http4s)\n* Contact us via the [http4s security policy](https://github.com/http4s/http4s/security/policy)",
  "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-client_2.12"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.21.29"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.21.28"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-client_2.12"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.22.0"
      }, {
        "fixed" : "0.22.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.22.4"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-client_2.12"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.23.0"
      }, {
        "fixed" : "0.23.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.23.3"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-client_2.13"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.21.29"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.21.28"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-client_2.13"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.22.0"
      }, {
        "fixed" : "0.22.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.22.4"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-client_2.13"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.23.0"
      }, {
        "fixed" : "0.23.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.23.3"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-client_3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.21.29"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.21.28"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-client_3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.22.0"
      }, {
        "fixed" : "0.22.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.22.4"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-client_3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.23.0"
      }, {
        "fixed" : "0.23.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.23.3"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-server_2.10"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "0.21.28"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-server_2.11"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "0.21.28"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-server_2.12"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.21.29"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.21.28"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-server_2.12"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.22.0"
      }, {
        "fixed" : "0.22.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.22.4"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-server_2.12"
    },
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      "type" : "ECOSYSTEM",
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        "introduced" : "0.23.0"
      }, {
        "fixed" : "0.23.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.23.3"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-server_2.13"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.21.29"
      } ]
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    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.21.28"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-server_2.13"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.22.0"
      }, {
        "fixed" : "0.22.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.22.4"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-server_2.13"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.23.0"
      }, {
        "fixed" : "0.23.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.23.3"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-server_2.13.0-M5"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "0.21.28"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-server_3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.22.0"
      }, {
        "fixed" : "0.22.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.22.4"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4s:http4s-server_3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.23.0"
      }, {
        "fixed" : "0.23.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.23.3"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/http4s/http4s/security/advisories/GHSA-5vcm-3xc3-w7x3"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-41084"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4s/http4s/commit/d02007db1da4f8f3df2dbf11f1db9ac7afc3f9d8"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/http4s/http4s"
  }, {
    "type" : "WEB",
    "url" : "https://httpwg.org/http-core/draft-ietf-httpbis-semantics-latest.html#fields.values"
  }, {
    "type" : "WEB",
    "url" : "https://owasp.org/www-community/attacks/HTTP_Response_Splitting"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-74", "CWE-918" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-09-21T16:10:13Z",
    "nvd_published_at" : "2021-09-21T18:15:00Z"
  }
}