Nokogiri is an open source XML and HTML library for the Ruby programming language. Prior to 1.19.4, calling Document#encoding= with an invalid encoding (e.g., a non-string, or a string containing a null byte) raises an exception, but only after freeing the document's current encoding string without replacing it. The document is left referencing freed memory, so the next call to Document#encoding reads invalid memory, which can cause a segfault or leak freed bytes into a Ruby String. Affects the CRuby (libxml2) implementation only; JRuby is not affected. This vulnerability is fixed in 1.19.4.

AMD. A buffer overflow issue was addressed with improved memory handling.

Severity

Nokogiri maintainers have evaluated this as Low Severity (CVSS3 2.6).

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::DEFAULTSCHEMA)

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(trustedschema, Nokogiri::XML::ParseOptions.new.nononet)

References

- This issue's public advisory - Original Hackerone report (private) - OWASP description of XXE attackProcessing) - OWASP description of SSRF attack

Credit

This vulnerability was independently reported by @eric-therond and @gucki.

The Nokogiri maintainers would like to thank HackerOne for providing a secure, responsible mechanism for reporting, and for providing their fantastic service to us.

Nokogiri is an open source XML and HTML library for the Ruby programming language. Prior to 1.19.4, Nokogiri::XML::NodeSet#[] (and its alias #slice) checked the requested index against the node set's bounds using a 32-bit-truncated copy of the index. A large negative index could pass the check and then be used at full width, reading outside the node set's storage. On CRuby this is an out-of-bounds read that typically crashes the process; on JRuby it is not memory-unsafe but returns an incorrect node. This vulnerability is fixed in 1.19.4.

Nokogiri is an open source XML and HTML library for the Ruby programming language. Prior to 1.19.4, Nokogiri’s CRuby native extension could leave a Ruby wrapper pointing to freed memory when replacing the value of an XML attribute. If Ruby code had already accessed an attribute child node, Nokogiri::XML::Attr#value= could free the underlying native child node while the wrapper remained reachable through the document node cache. A later use of the freed child node or a Ruby GC mark could dereference an invalid pointer, causing an invalid read and a possible segfault. This vulnerability is fixed in 1.19.4.

Nokogiri is an open source XML and HTML library for the Ruby programming language. Prior to 1.19.4, Nokogiri contains a bug when calling certain methods on allocated-but-uninitialized native wrapper classes that inherit from Nokogiri::XML::Node. This caused a NULL pointer dereference that could crash the process. This vulnerability is fixed in 1.19.4.

Nokogiri is an open source XML and HTML library for the Ruby programming language. Prior to 1.19.4, Nokogiri::XML::Document#root= validated only that the new root was a Nokogiri::XML::Node, allowing a DTD node to be set as the document root. The result is a heap use-after-free during garbage collection or finalization, leading to an invalid memory read or potentially a segfault. This vulnerability is fixed in 1.19.4.

Nokogiri is an open source XML and HTML library for the Ruby programming language. Prior to 1.19.4, Nokogiri::XML::XPathContext did not keep its source document alive for garbage collection. If an XPathContext outlived its document and the document was collected, evaluating an XPath expression could read invalid memory and potentially segfault. This is only reachable when application code constructs an XPathContext directly and lets the document become unreachable while continuing to use the context. The normal Document#xpath, #css, and related search methods are not affected, and it is not triggerable by malicious document input. This vulnerability is fixed in 1.19.4.

Nokogiri is an open source XML and HTML library for the Ruby programming language. Prior to 1.19.4, XInclude substitution performed by Nokogiri::XML::Node#doxinclude replaced each <xi:include> in place, freeing the include node along with its children (such as <xi:fallback> and its descendants) and any namespaces declared on them. If an application had already exposed one of those nodes or namespaces to Ruby, the corresponding Ruby object was left pointing at freed memory. Using the object could result in invalid reads or writes to memory. This vulnerability is fixed in 1.19.4.

Nokogiri is an open source XML and HTML library for the Ruby programming language. Prior to 1.19.4, the NONET parse option, which Nokogiri turns on by default for Nokogiri::XML::Schema (see CVE-2020-26247), was not correctly enforced on the JRuby implementation. As a result, a schema parsed with default options could still cause external resources to be fetched over the network, potentially enabling SSRF or XXE attacks. This vulnerability is fixed in 1.19.4.

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.)

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.

Summary

Nokogiri < v1.13.6 does not type-check all inputs into the XML and HTML4 SAX parsers. For CRuby users, this may allow specially crafted untrusted inputs to cause illegal memory access errors (segfault) or reads from unrelated memory.

Severity

The Nokogiri maintainers have evaluated this as High 8.2 (CVSS3.1).

Mitigation

CRuby users should upgrade to Nokogiri >= 1.13.6.

JRuby users are not affected.

Workarounds

To avoid this vulnerability in affected applications, ensure the untrusted input is a String by calling #tos or equivalent.

Credit

This vulnerability was responsibly reported by @agustingianni and the Github Security Lab.