CVE-2021-41098

Improper Restriction of XML External Entity Reference (XXE) in Nokogiri on JRuby

Severity

The Nokogiri maintainers have evaluated this as High Severity 7.5 (CVSS3.0) for JRuby users. (This security advisory does not apply to CRuby users.)

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.

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

An XML parser processes external entity references in untrusted input, causing the server to fetch internal resources or remote URLs. Typical impact: local file disclosure, server-side request forgery, or denial of service.

CVE-2021-41098 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.12.5); upgrading removes the vulnerable code path.

Kodem intelligence

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1. What is CVE-2021-41098? CVE-2021-41098 is a high-severity XML external entity injection (XXE) vulnerability in nokogiri (rubygems), affecting versions <= 1.12.4. It is fixed in 1.12.5. An XML parser processes external entity references in untrusted input, causing the server to fetch internal resources or remote URLs.
2. How severe is CVE-2021-41098? CVE-2021-41098 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of nokogiri are affected by CVE-2021-41098? nokogiri (rubygems) versions <= 1.12.4 is affected.
4. Is there a fix for CVE-2021-41098? Yes. CVE-2021-41098 is fixed in 1.12.5. Upgrade to this version or later.
5. Is CVE-2021-41098 exploitable, and should I be worried? Whether CVE-2021-41098 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2021-41098 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2021-41098? Upgrade nokogiri to 1.12.5 or later.

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