How severe is GHSA-c4rq-3m3g-8wgx?

GHSA-c4rq-3m3g-8wgx has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by GHSA-c4rq-3m3g-8wgx?

GHSA-c4rq-3m3g-8wgx affects the following packages: nokogiri (RubyGems). Ecosystems affected: RubyGems.

How do I fix GHSA-c4rq-3m3g-8wgx?

Update nokogiri to 1.19.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-c4rq-3m3g-8wgx is resolved across your whole dependency graph.

How do I detect GHSA-c4rq-3m3g-8wgx in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nokogiri. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate GHSA-c4rq-3m3g-8wgx if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against GHSA-c4rq-3m3g-8wgx?

O3 pinpoints whether GHSA-c4rq-3m3g-8wgx is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is GHSA-c4rq-3m3g-8wgx actively exploited in the wild?

No public exploit code has been indexed for GHSA-c4rq-3m3g-8wgx yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was GHSA-c4rq-3m3g-8wgx published, and has it been updated?

GHSA-c4rq-3m3g-8wgx was published on May 6, 2026 and was last updated on May 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎 RubyGems

GHSA-c4rq-3m3g-8wgx

HIGH

Nokogiri CSS selector tokenizer has regular expression backtracking

Published

May 6, 2026

Updated

May 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Blast Radius

1 pkg affected

💎nokogiri

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

Summary

Nokogiri's CSS selector tokenizer contains regular expressions whose construction may result in exponential regex backtracking on adversarial selectors. Three ReDoS vectors are addressed in this release:

String-literal tokenization on certain unterminated quoted-string input.
String-literal tokenization on a separate class of hex-escape-rich input.
Identifier tokenization on hex-escape-rich input.

The public CSS selector methods that funnel through the affected tokenizer are Nokogiri::CSS.xpath_for, Node#css, Node#at_css, Searchable#search, and CSS::Parser#parse.

Mitigation

Upgrade to Nokogiri >= 1.19.3.

If users are unable to upgrade, two options are available:

Avoid the use of attacker-controlled text in CSS selectors. Applications that only pass developer-authored selectors to Nokogiri are not directly exposed.
Set global Regexp.timeout (Ruby 3.2+, JRuby 9.4+) to bound parse time.

Severity

The Nokogiri maintainers have evaluated this as High Severity (CVSS 7.5, AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

An attacker able to inject user-supplied text into a CSS selector parse method can cause exponential backtracking, resulting in a potential denial of service.

Resources

CWE-1333: Inefficient Regular Expression Complexity

Credit

Vector 1 was responsibly reported by @colby-swandale. Vectors 2 and 3 were discovered by @flavorjones during the response to the original report.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`nokogiri`	all versions	1.19.3

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nokogiri. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update nokogiri to 1.19.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-c4rq-3m3g-8wgx is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-c4rq-3m3g-8wgx is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to GHSA-c4rq-3m3g-8wgx. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

## Summary Nokogiri's CSS selector tokenizer contains regular expressions whose construction may result in exponential regex backtracking on adversarial selectors. Three ReDoS vectors are addressed in this release: 1. String-literal tokenization on certain unterminated quoted-string input. 2. String-literal tokenization on a separate class of hex-escape-rich input. 3. Identifier tokenization on hex-escape-rich input. The public CSS selector methods that funnel through the affected tokenizer are `Nokogiri::CSS.xpath_for`, `Node#css`, `Node#at_css`, `Searchable#search`, and `CSS::Parser#parse

O3 Security · Impact-Aware SCA

Is GHSA-c4rq-3m3g-8wgx in your dependencies?

O3 detects GHSA-c4rq-3m3g-8wgx across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works