CWE
611 918
Advisory Published
Advisory Published
Updated

CVE-2020-26247: XXE in Nokogiri

First published: Wed Dec 30 2020(Updated: )

### Severity Nokogiri 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). ### Description In 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. This behavior is counter to the security policy followed by Nokogiri maintainers, which is to treat all input as **untrusted** by default whenever possible. Please 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". ### Affected Versions Nokogiri `<= 1.10.10` as well as prereleases `1.11.0.rc1`, `1.11.0.rc2`, and `1.11.0.rc3` ### Mitigation There are no known workarounds for affected versions. Upgrade to Nokogiri `1.11.0.rc4` or later. If, 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): 1. Ensure the input is trusted. Do not enable this option for untrusted input. 2. When invoking the `Nokogiri::XML::Schema` constructor, pass as the second parameter an instance of `Nokogiri::XML::ParseOptions` with the `NONET` flag turned off. So if your previous code was: ``` ruby # in v1.11.0.rc3 and earlier, this call allows resources to be accessed over the network # but in v1.11.0.rc4 and later, this call will disallow network access for external resources schema = Nokogiri::XML::Schema.new(schema) # in v1.11.0.rc4 and later, the following is equivalent to the code above # (the second parameter is optional, and this demonstrates its default value) schema = Nokogiri::XML::Schema.new(schema, Nokogiri::XML::ParseOptions::DEFAULT_SCHEMA) ``` Then you can add the second parameter to indicate that the input is trusted by changing it to: ``` ruby # in v1.11.0.rc3 and earlier, this would raise an ArgumentError # but in v1.11.0.rc4 and later, this allows resources to be accessed over the network schema = Nokogiri::XML::Schema.new(trusted_schema, Nokogiri::XML::ParseOptions.new.nononet) ``` ### References - [This issue's public advisory](https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-vr8q-g5c7-m54m) - [Original Hackerone report (private)](https://hackerone.com/reports/747489) - [OWASP description of XXE attack](https://www.owasp.org/index.php/XML_External_Entity_(XXE)_Processing) - [OWASP description of SSRF attack](https://www.owasp.org/index.php/Server_Side_Request_Forgery) ### Credit This vulnerability was independently reported by @eric-therond and @gucki. The 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.

Credit: security-advisories@github.com security-advisories@github.com

Affected SoftwareAffected VersionHow to fix
rubygems/nokogiri<=1.10.10
1.11.0
<1.11.0
=1.11.0-rc1
=1.11.0-rc2
=1.11.0-rc3
=9.0
=10.0
Nokogiri Nokogiri<1.11.0
Nokogiri Nokogiri=1.11.0-rc1
Nokogiri Nokogiri=1.11.0-rc2
Nokogiri Nokogiri=1.11.0-rc3
Debian Debian Linux=9.0
Debian Debian Linux=10.0
redhat/rubygem-nokogiri<1.11.0.
1.11.0.

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Frequently Asked Questions

  • What is the severity of CVE-2020-26247?

    The severity of CVE-2020-26247 is Low (CVSS3 2.6).

  • How does CVE-2020-26247 affect Nokogiri?

    CVE-2020-26247 affects Nokogiri versions <= 1.11.0.rc3.

  • What is the remedy for CVE-2020-26247?

    The remedy for CVE-2020-26247 is to update Nokogiri to version 1.11.0.

  • What is the reference for CVE-2020-26247?

    The references for CVE-2020-26247 are: [GitHub Advisory](https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-vr8q-g5c7-m54m), [GitHub Commit](https://github.com/sparklemotion/nokogiri/commit/9c87439d9afa14a365ff13e73adc809cb2c3d97b), [HackerOne Report](https://hackerone.com/reports/747489).

  • What is the Common Weakness Enumeration (CWE) associated with CVE-2020-26247?

    The Common Weakness Enumeration (CWE) associated with CVE-2020-26247 are CWE-918 and CWE-611.

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