CVE-2026-79770
Description
A flaw was found in Nokogiri. A remote attacker can inject specially crafted CSS selectors into methods such as Node#css or Node#at_css. This injection can lead to regular expression denial of service (ReDoS) due to exponential regex backtracking, causing the application to become unresponsive.
Statement
A Regular Expression Denial of Service (ReDoS) vulnerability was discovered in Nokogiri's CSS selector tokenizer. 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.
Mitigation
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.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU)
Attackers can create crafted inputs that intentionally cause the regular expression to use excessive backtracking in a way that causes the CPU consumption to spike.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
