CVE-2026-79770: Nokogiri Nokogiri CSS Selector Tokenizer Has Vulnerability

HIGH
Advisory Identifier: GHSA-c4rq-3m3g-8wgx
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CVSS 7.5
CWE-1333
Published
Advisory Summary

CVE-2026-79770 is a HIGH (CVSS 7.5) nokogiri css selector tokenizer has vulnerability (CWE-1333: Inefficient Regular Expression Complexity) affecting Nokogiri libraries in the RubyGems ecosystem. The issue involves nokogiri css selector tokenizer has regular expression backtracking. Remediation is available by upgrading affected packages to version 1.19.3.

CVE-2026-79770 at a Glance

CVE Identifier CVE-2026-79770
GHSA Identifier GHSA-c4rq-3m3g-8wgx
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-1333: Inefficient Regular Expression Complexity
Affected Product Nokogiri
Package Ecosystem RubyGems
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-79770

To remediate this vulnerability, upgrade all affected Nokogiri dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

nokogiri fixed: 1.19.3 
Upgrade nokogiri to 1.19.3
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for nokogiri

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-79770, inspect your project dependencies for Nokogiri:

inspect dependencies for nokogiri

Analyze the terminal output to locate any version of Nokogiri in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.19.3), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1333: Inefficient Regular Expression Complexity, where the product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential. In Nokogiri, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## 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`. ## 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](https://cwe.mitre.org/data/definitions/1333.html) ## Credit Vector 1 was responsibly reported by @colby-swandale. Vectors 2 and 3 were discovered by @flavorjones during the response to the original report.

CVE-2026-79770 Affected Nokogiri Versions

1 component(s)
Fixed Versions:
1.19.3
Product / Package Ecosystem Affected Versions Fixed Version
nokogiri
gem/nokogiri
RubyGems
< 1.19.3
1.19.3

References

GitHub Advisory / Wiki ADVISORY
https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-c4rq-3m3g-8wgx
NVD — CVE-2026-79770 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-79770
Nokogiri Source Repository REPOSITORY
https://github.com/sparklemotion/nokogiri
www.vulncheck.com/advisories/nokogiri... WEB
https://www.vulncheck.com/advisories/nokogiri-before-redos-via-css-selector-tokenizer

Frequently Asked Questions

What is CVE-2026-79770?
CVE-2026-79770 is a security vulnerability in Nokogiri involving Nokogiri CSS selector tokenizer has regular expression backtracking under CWE-1333: Inefficient Regular Expression Complexity.
Which Nokogiri versions are affected?
Affected versions include releases prior to 1.19.3 across affected packages: nokogiri.
What version fixes CVE-2026-79770?
Upgrading to 1.19.3 (or the latest patched release for your respective branch) resolves the vulnerability.
Is nokogiri affected?
Yes, nokogiri is affected in releases prior to 1.19.3. Upgrade your dependency to 1.19.3 or later.
What is the CVSS score of CVE-2026-79770?
CVE-2026-79770 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-79770?
CVE-2026-79770 is classified under CWE-1333: Inefficient Regular Expression Complexity (The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.).
How can I check RubyGems dependencies for CVE-2026-79770?
Run the dependency tree command: 'inspect dependencies for nokogiri'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-c4rq-3m3g-8wgx",
  "modified" : "2026-09-02T14:43:29Z",
  "published" : "2026-05-06T18:24:18Z",
  "aliases" : [ "CVE-2026-79770" ],
  "summary" : "Nokogiri CSS selector tokenizer has regular expression backtracking",
  "details" : "## Summary\n\nNokogiri'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:\n\n1. String-literal tokenization on certain unterminated quoted-string input.\n2. String-literal tokenization on a separate class of hex-escape-rich input.\n3. Identifier tokenization on hex-escape-rich input.\n\nThe 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`.\n\n\n## Mitigation\n\nUpgrade to Nokogiri `>= 1.19.3`.\n\nIf users are unable to upgrade, two options are available:\n\n- Avoid the use of attacker-controlled text in CSS selectors. Applications that only pass developer-authored selectors to Nokogiri are not directly exposed.\n- Set global `Regexp.timeout` (Ruby 3.2+, JRuby 9.4+) to bound parse time.\n\n## Severity\n\nThe 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`).\n\nAn attacker able to inject user-supplied text into a CSS selector parse method can cause exponential backtracking, resulting in a potential denial of service.\n\n\n## Resources\n\n- [CWE-1333: Inefficient Regular Expression Complexity](https://cwe.mitre.org/data/definitions/1333.html)\n\n\n## Credit\n\nVector 1 was responsibly reported by @colby-swandale. Vectors 2 and 3 were discovered by @flavorjones during the response to the original report.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "nokogiri"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.19.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-c4rq-3m3g-8wgx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-79770"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/sparklemotion/nokogiri"
  }, {
    "type" : "WEB",
    "url" : "https://www.vulncheck.com/advisories/nokogiri-before-redos-via-css-selector-tokenizer"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1333" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-06T18:24:18Z",
    "nvd_published_at" : null
  }
}