High [CVE-2026-79770] Denial of Service via crafted CSS selectors
This high-severity Red Hat Linux advisory covers CVE-2026-79770.
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Summary
Nokogiri versions before 1.19.3 contain regular expression denial of service vulnerabilities in the CSS selector tokenizer affecting string-literal and identifier tokenization. Attackers can inject adversarial CSS selectors into methods like Node#css, Node#at_css, and Searchable#search to cause exponential regex backtracking and denial of service.
A flaw was found in Nokogiri. This injection can lead to regular expression denial of service (ReDoS) due to exponential regex backtracking, causing the application to become unresponsive.
When processing untrusted user input passed to methods like Node#css, Node#at_css, or Searchable#search, an attacker can inject adversarial CSS selectors containing malicious string literals or identifiers.
This triggers exponential regex backtracking within the parser, causing severe CPU exhaustion and leading to a Denial of Service (DoS) for the application thread. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
Weakness: CWE-1333. Red Hat lists Red Hat 3scale API Management Platform 2; Red Hat Satellite 6 as not affected.
- < 1.19.3
Official advisory · high-confidence parse· fetched 13 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 13 days ago·verify at source
Mitigation checklist
- Do not pass untrusted user input directly into Nokogiri CSS search methods. If dynamic querying is necessary, sanitize input or restrict query parameter patterns before evaluation.
Official advisory · high-confidence parse· fetched 13 days ago·verify at source
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