CVE-2021-41098: Nokogiri Improper Restriction Of XML External Vulnerability

HIGH
Advisory Identifier: GHSA-2rr5-8q37-2w7h
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CVSS 7.5
CWE-611
Published
Advisory Summary

CVE-2021-41098 is a HIGH (CVSS 7.5) improper restriction of xml external vulnerability (CWE-611: Improper Restriction of XML External Entity Reference) affecting Nokogiri libraries in the RubyGems ecosystem. The issue involves improper restriction of xml external entity reference (xxe) in nokogiri on jruby. Remediation is available by upgrading affected packages to version 1.12.5.

CVE-2021-41098 at a Glance

CVE Identifier CVE-2021-41098
GHSA Identifier GHSA-2rr5-8q37-2w7h
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-611: Improper Restriction of XML External Entity Reference
Affected Product Nokogiri
Package Ecosystem RubyGems
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2021-41098

To remediate this vulnerability, upgrade all affected Nokogiri dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

nokogiri fixed: 1.12.5 
Upgrade nokogiri to 1.12.5
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for nokogiri

How to Check if You Are Affected

To determine whether your application is affected by CVE-2021-41098, inspect your project dependencies for Nokogiri:

inspect dependencies for nokogiri

Analyze the terminal output to locate any version of Nokogiri in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.12.5), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-611: Improper Restriction of XML External Entity Reference, where the product processes an xml document that can contain xml entities with uris that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output. In Nokogiri, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Severity The Nokogiri maintainers have evaluated this as [**High Severity** 7.5 (CVSS3.0)](https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N/E:H/RL:O/RC:C/MAV:N/MAC:L) for JRuby users. (This security advisory does not apply to CRuby users.) ### Impact In Nokogiri v1.12.4 and earlier, **on JRuby only**, the SAX parser resolves external entities by default. Users of Nokogiri on JRuby who parse untrusted documents using any of these classes are affected: - Nokogiri::XML::SAX::Parser - Nokogiri::HTML4::SAX::Parser or its alias Nokogiri::HTML::SAX::Parser - Nokogiri::XML::SAX::PushParser - Nokogiri::HTML4::SAX::PushParser or its alias Nokogiri::HTML::SAX::PushParser ### Mitigation JRuby users should upgrade to Nokogiri v1.12.5 or later. There are no workarounds available for v1.12.4 or earlier. CRuby users are not affected.

CVE-2021-41098 Affected Nokogiri Versions

1 component(s)
Fixed Versions:
1.12.5
Product / Package Ecosystem Affected Versions Fixed Version
nokogiri
gem/nokogiri
RubyGems
< 1.12.5
1.12.5

References

GitHub Advisory / Wiki ADVISORY
https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-2rr5-8q37-2w7h
NVD — CVE-2021-41098 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-41098
Security Fix Commit FIX COMMIT
https://github.com/sparklemotion/nokogiri/commit/5bf729ff3cc84709ee3c3248c981584088bf9f6d
Nokogiri Source Repository REPOSITORY
https://github.com/rubysec/ruby-advisory-db/blob/master/gems/nokogiri/CVE-2021-41098.yml
Nokogiri Source Repository REPOSITORY
https://github.com/sparklemotion/nokogiri

Frequently Asked Questions

What is CVE-2021-41098?
CVE-2021-41098 is a security vulnerability in Nokogiri involving Improper Restriction of XML External Entity Reference (XXE) in Nokogiri on JRuby under CWE-611: Improper Restriction of XML External Entity Reference.
Which Nokogiri versions are affected?
Affected versions include releases prior to 1.12.5 across affected packages: nokogiri.
What version fixes CVE-2021-41098?
Upgrading to 1.12.5 (or the latest patched release for your respective branch) resolves the vulnerability.
Is nokogiri affected?
Yes, nokogiri is affected in releases prior to 1.12.5. Upgrade your dependency to 1.12.5 or later.
What is the CVSS score of CVE-2021-41098?
CVE-2021-41098 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
What CWE is associated with CVE-2021-41098?
CVE-2021-41098 is classified under CWE-611: Improper Restriction of XML External Entity Reference (The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.).
How can I check RubyGems dependencies for CVE-2021-41098?
Run the dependency tree command: 'inspect dependencies for nokogiri'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2rr5-8q37-2w7h",
  "modified" : "2021-09-28T18:46:02Z",
  "published" : "2021-09-27T20:12:47Z",
  "aliases" : [ "CVE-2021-41098" ],
  "summary" : "Improper Restriction of XML External Entity Reference (XXE) in Nokogiri on JRuby",
  "details" : "### Severity\n\nThe Nokogiri maintainers have evaluated this as [**High Severity** 7.5 (CVSS3.0)](https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N/E:H/RL:O/RC:C/MAV:N/MAC:L) for JRuby users. (This security advisory does not apply to CRuby users.)\n\n\n### Impact\n\nIn Nokogiri v1.12.4 and earlier, **on JRuby only**, the SAX parser resolves external entities by default.\n\nUsers of Nokogiri on JRuby who parse untrusted documents using any of these classes are affected:\n\n- Nokogiri::XML::SAX::Parser\n- Nokogiri::HTML4::SAX::Parser or its alias Nokogiri::HTML::SAX::Parser\n- Nokogiri::XML::SAX::PushParser\n- Nokogiri::HTML4::SAX::PushParser or its alias Nokogiri::HTML::SAX::PushParser\n\n\n### Mitigation\n\nJRuby users should upgrade to Nokogiri v1.12.5 or later. There are no workarounds available for v1.12.4 or earlier.\n\nCRuby users are not affected.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "nokogiri"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.12.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.12.4"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-2rr5-8q37-2w7h"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-41098"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sparklemotion/nokogiri/commit/5bf729ff3cc84709ee3c3248c981584088bf9f6d"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/nokogiri/CVE-2021-41098.yml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/sparklemotion/nokogiri"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-611" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-09-27T19:20:23Z",
    "nvd_published_at" : "2021-09-27T20:15:00Z"
  }
}