CVE-2020-26247: Nokogiri :XML::Schema Trusts Input By Default, Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-vr8q-g5c7-m54m",
  "modified" : "2022-08-16T19:53:40Z",
  "published" : "2020-12-30T18:35:06Z",
  "aliases" : [ "CVE-2020-26247" ],
  "summary" : "Nokogiri::XML::Schema trusts input by default, exposing risk of XXE vulnerability",
  "details" : "### Severity\n\nNokogiri maintainers have evaluated this as [__Low Severity__ (CVSS3 2.6)](https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:N/A:N).\n\n\n### Description\n\nIn Nokogiri versions <= 1.11.0.rc3, XML Schemas parsed by `Nokogiri::XML::Schema` are **trusted** by default, allowing external resources to be accessed over the network, potentially enabling XXE or SSRF attacks.\n\nThis behavior is counter to the security policy followed by Nokogiri maintainers, which is to treat all input as **untrusted** by default whenever possible.\n\nPlease note that this security fix was pushed into a new minor version, 1.11.x, rather than a patch release to the 1.10.x branch, because it is a breaking change for some schemas and the risk was assessed to be \"Low Severity\".\n\n\n### Affected Versions\n\nNokogiri `<= 1.10.10` as well as prereleases `1.11.0.rc1`, `1.11.0.rc2`, and `1.11.0.rc3`\n\n\n### Mitigation\n\nThere are no known workarounds for affected versions. Upgrade to Nokogiri `1.11.0.rc4` or later.\n\nIf, after upgrading to `1.11.0.rc4` or later, you wish to re-enable network access for resolution of external resources (i.e., return to the previous behavior):\n\n1. Ensure the input is trusted. Do not enable this option for untrusted input.\n2. When invoking the `Nokogiri::XML::Schema` constructor, pass as the second parameter an instance of `Nokogiri::XML::ParseOptions` with the `NONET` flag turned off.\n\nSo if your previous code was:\n\n``` ruby\n# in v1.11.0.rc3 and earlier, this call allows resources to be accessed over the network\n# but in v1.11.0.rc4 and later, this call will disallow network access for external resources\nschema = Nokogiri::XML::Schema.new(schema)\n\n# in v1.11.0.rc4 and later, the following is equivalent to the code above\n# (the second parameter is optional, and this demonstrates its default value)\nschema = Nokogiri::XML::Schema.new(schema, Nokogiri::XML::ParseOptions::DEFAULT_SCHEMA)\n```\n\nThen you can add the second parameter to indicate that the input is trusted by changing it to:\n\n``` ruby\n# in v1.11.0.rc3 and earlier, this would raise an ArgumentError \n# but in v1.11.0.rc4 and later, this allows resources to be accessed over the network\nschema = Nokogiri::XML::Schema.new(trusted_schema, Nokogiri::XML::ParseOptions.new.nononet)\n```\n\n\n### References\n\n- [This issue's public advisory](https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-vr8q-g5c7-m54m)\n- [Original Hackerone report (private)](https://hackerone.com/reports/747489)\n- [OWASP description of XXE attack](https://www.owasp.org/index.php/XML_External_Entity_(XXE)_Processing)\n- [OWASP description of SSRF attack](https://www.owasp.org/index.php/Server_Side_Request_Forgery)\n\n\n### Credit \n\nThis vulnerability was independently reported by @eric-therond and @gucki.\n\nThe Nokogiri maintainers would like to thank [HackerOne](https://hackerone.com/nokogiri) for providing a secure, responsible mechanism for reporting, and for providing their fantastic service to us.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "nokogiri"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.11.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.10.10"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-vr8q-g5c7-m54m"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-26247"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sparklemotion/nokogiri/commit/9c87439d9afa14a365ff13e73adc809cb2c3d97b"
  }, {
    "type" : "WEB",
    "url" : "https://hackerone.com/reports/747489"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/nokogiri/CVE-2020-26247.yml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/sparklemotion/nokogiri"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md#v1110--2021-01-03"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sparklemotion/nokogiri/releases/tag/v1.11.0.rc4"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2021/06/msg00007.html"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2022/10/msg00018.html"
  }, {
    "type" : "WEB",
    "url" : "https://rubygems.org/gems/nokogiri"
  }, {
    "type" : "WEB",
    "url" : "https://security.gentoo.org/glsa/202208-29"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-611" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2020-12-30T18:34:51Z",
    "nvd_published_at" : "2020-12-30T19:15:00Z"
  }
}