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
Credit
Vector 1 was responsibly reported by @colby-swandale. Vectors 2 and 3 were discovered by @flavorjones during the response to the original report.
References
colby-swandale Reporter
flavorjones Remediation developer
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:
The public CSS selector methods that funnel through the affected tokenizer are
Nokogiri::CSS.xpath_for,Node#css,Node#at_css,Searchable#search, andCSS::Parser#parse.Mitigation
Upgrade to Nokogiri
>= 1.19.3.If users are unable to upgrade, two options are available:
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.
References