BREW-MIKUTTER-CVE-2026-79770 (GHSA-C4RQ-3M3G-8WGX)
Vulnerability from osv_homebrew – Published: 2026-08-27 12:38 – Updated: 2026-10-07 22:55 – Source websiteSummary
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
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": [
{
"ecosystem_specific": {
"fix": null,
"range_state": "affected",
"resource": "nokogiri",
"resource_purl": "pkg:gem/nokogiri@1.16.3",
"upstream_fixed_in": "1.19.3"
},
"package": {
"ecosystem": "Homebrew",
"name": "mikutter",
"purl": "pkg:brew/mikutter"
},
"ranges": [
{
"events": [
{
"introduced": "3.4.6"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "RubyGems",
"key": "pkg:gem/nokogiri@1.16.3",
"name": "nokogiri",
"resource": "nokogiri",
"strategy": "registry",
"subject_version": "1.16.3"
}
]
},
"details": "## Summary\n\nNokogiri\u0027s 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 `\u003e= 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.",
"id": "BREW-mikutter-CVE-2026-79770",
"modified": "2026-10-07T22:55:09Z",
"published": "2026-08-27T12:38:44Z",
"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"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
],
"summary": "Nokogiri CSS selector tokenizer has regular expression backtracking",
"upstream": [
"GHSA-c4rq-3m3g-8wgx",
"CVE-2026-79770"
]
}
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