Summary
Nokogiri: Possible Use-After-Free when Nokogiri::XML::Document#encoding= raises an exception
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.
Severity
The Nokogiri maintainers have evaluated this as low severity. Reaching it requires an unusual API-usage pattern that does not arise during normal use. The application must pass an invalid encoding to Document#encoding=, rescue the resulting exception, and then continue using the same document. Nokogiri 1.19.4 makes this pattern safe with no change to the public API. The document no longer references freed memory after the exception is raised.
Mitigation
Upgrade to Nokogiri 1.19.4 or later.
If users are unable to upgrade, avoid passing attacker-controlled values to Document#encoding=. Applications that only assign developer-authored encodings are not directly exposed.
Credit
This issue was responsibly reported by Zheng Yu from depthfirst.com.
Impact
Memory is accessed after it has been freed, leading to undefined behavior in native code. Typical impact: memory corruption, crash, or potential code execution.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is GHSA-5V8H-3H3Q-446P? GHSA-5V8H-3H3Q-446P is a low-severity use after free vulnerability in nokogiri (rubygems), affecting versions < 1.19.4. It is fixed in 1.19.4. Memory is accessed after it has been freed, leading to undefined behavior in native code.
- Which versions of nokogiri are affected by GHSA-5V8H-3H3Q-446P? nokogiri (rubygems) versions < 1.19.4 is affected.
- Is there a fix for GHSA-5V8H-3H3Q-446P? Yes. GHSA-5V8H-3H3Q-446P is fixed in 1.19.4. Upgrade to this version or later.
- Is GHSA-5V8H-3H3Q-446P exploitable, and should I be worried? Whether GHSA-5V8H-3H3Q-446P is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether GHSA-5V8H-3H3Q-446P is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix GHSA-5V8H-3H3Q-446P? Upgrade
nokogirito 1.19.4 or later.