Executive Summary

The CVE-2026-57234 vulnerability affects the Nokogiri library, specifically its XML::Schema implementation on JRuby. The issue involves the NONET parse option, which is intended to prevent network requests during schema parsing but was not properly enforced on JRuby. This flaw allowed external resources to be fetched over the network despite the NONET setting, potentially enabling Server-Side Request Forgery (SSRF) or XML External Entity (XXE) attacks.

The vulnerability bypasses a previous fix (CVE-2020-26247) that addressed a similar issue in CRuby but not JRuby. The fix in Nokogiri 1.19.4 replaces the scheme denylist with an allowlist, ensuring only local resources are resolved when NONET is enabled, aligning JRuby's behavior with CRuby.

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Impact Analysis

This vulnerability can impact you by allowing an attacker to cause your application to fetch external resources over the network when parsing XML schemas, even if the NONET option is enabled. This can lead to Server-Side Request Forgery (SSRF) or XML External Entity (XXE) attacks.

Such attacks could be used to access internal systems, leak sensitive information, or cause denial of service. However, the severity is rated as low (CVSS 2.6) because exploitation requires specific conditions such as untrusted input and user interaction.

Users are advised to upgrade to Nokogiri 1.19.4 or later to mitigate this risk.

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Detection Guidance

This vulnerability involves Nokogiri's XML::Schema implementation on JRuby improperly enforcing the NONET parse option, allowing external network requests during schema parsing. Detection would involve monitoring for unexpected outbound network requests initiated by Nokogiri processes, especially during XML schema parsing.

Since the issue is specific to JRuby and Nokogiri versions prior to 1.19.4, you can check the Nokogiri version in your environment to identify if you are vulnerable.

• Check Nokogiri version: `gem list nokogiri` or within JRuby environment `jruby -S gem list nokogiri`
• Monitor network traffic for unexpected outbound connections from JRuby processes, for example using `tcpdump` or `netstat`:
• `sudo tcpdump -i any host <suspicious_external_resource>`
• `netstat -plant | grep jruby` to identify active network connections from JRuby

Additionally, review application logs for XML schema parsing operations that might be triggering external resource fetches.

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Mitigation Strategies

The primary mitigation step is to upgrade Nokogiri to version 1.19.4 or later, where the vulnerability is fixed by properly enforcing the NONET parse option on JRuby.

If upgrading immediately is not possible, ensure that the NONET option is enabled explicitly when parsing XML schemas to prevent network access, although prior versions may not enforce this correctly on JRuby.

Avoid processing untrusted XML input or schemas that could trigger external network requests.

If network access is necessary for trusted input, the NONET option can be disabled explicitly, but this is not recommended for untrusted data.

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Compliance Impact

The vulnerability in Nokogiri's XML::Schema implementation on JRuby could potentially enable SSRF or XXE attacks by allowing external resources to be fetched during schema parsing. Such attacks can lead to unauthorized access to internal resources or data exfiltration.

While the CVE description and resources do not explicitly mention compliance with standards like GDPR or HIPAA, vulnerabilities that enable SSRF or XXE attacks can pose risks to data confidentiality and integrity, which are critical aspects of these regulations.

Therefore, if exploited, this vulnerability could impact compliance by exposing sensitive data or systems to unauthorized access, potentially violating data protection requirements under regulations such as GDPR or HIPAA.

Upgrading to Nokogiri 1.19.4 or later, which fixes the issue, is recommended to mitigate these risks and help maintain compliance.

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