CVE-2026-57436 Nokogiri: Possible Use-After-Free when setting `Document#root=` to an invalid node type

What is CVE-2026-57436?

CVE-2026-57436 is a low-severity use after free vulnerability in sparklemotion nokogiri, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

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.

Weakness: CWE-416

Which versions are affected by CVE-2026-57436?

2 open source packages ship an affected version, including nokogiri. It affects 1 product.

Products include Nokogiri Nokogiri.

How do I fix CVE-2026-57436?

Upgrade nokogiri to 1.19.4 or later.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2026-57436 being exploited?

There is no known exploitation of CVE-2026-57436 in the wild and no public exploit code.

Other vulnerabilities in sparklemotion nokogiri

• CVE-2026-79770 Nokogiri before 1.19.3 ReDoS via CSS selector tokenizer High 8.7
• CVE-2022-23476 Unchecked return value from xmlTextReaderExpand in Nokogiri High 7.5
• CVE-2021-41098 Improper Restriction of XML External Entity Reference (XXE) in Nokogiri on JRuby High 7.5
• CVE-2012-6685 Nokogiri is vulnerable to XML External Entity (XXE) attack High 7.5
• CVE-2026-79771 Nokogiri before 1.19.3 Memory Leak via XSLT Transform Medium 6.9

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-91077, BELL-CVE-2026-57436, CLEANSTART-2026-VY28909, DEBIAN-CVE-2026-57436, GHSA-wjv4-x9w8-wm3h, MINI-2prj-6444-hg9w and 8 more.