CVE-2026-57236 Nokogiri: Possible Use-After-Free when `Nokogiri::XML::Document#encoding=` raises an exception
Attackers can trigger a use-after-free in Nokogiri by passing invalid encodings, causing crashes or leaking memory in Ruby applications.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-57236?
CVE-2026-57236 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, 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.
Weakness: CWE-416
Which versions are affected by CVE-2026-57236?
2 open source packages ship an affected version, including nokogiri. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
nokogiri RubyGems | All versions | 1.19.4 |
nokogiri RubyGems | All versions | 1.19.4 |
Products include Nokogiri Nokogiri.
How do I fix CVE-2026-57236?
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-2026-57236 being exploited?
There is no known exploitation of CVE-2026-57236 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
- CVE-2022-23476 Unchecked return value from xmlTextReaderExpand in Nokogiri
- CVE-2021-41098 Improper Restriction of XML External Entity Reference (XXE) in Nokogiri on JRuby
- CVE-2012-6685 Nokogiri is vulnerable to XML External Entity (XXE) attack
- CVE-2026-79771 Nokogiri before 1.19.3 Memory Leak via XSLT Transform
Sources
Also known as AZL-91068, BELL-CVE-2026-57236, CLEANSTART-2026-TY62562, DEBIAN-CVE-2026-57236, GHSA-5v8h-3h3q-446p, MINI-6mm4-28v8-w62c and 8 more.