How severe is CVE-2026-79770?

No CVSS score has been assigned to CVE-2026-79770 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-79770?

CVE-2026-79770 affects the following packages: nokogiri (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2026-79770?

Update nokogiri to 1.19.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-79770 is resolved across your whole dependency graph.

How do I detect CVE-2026-79770 in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nokogiri, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-79770 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-79770 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-79770 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-79770?

CVE-2026-79770 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 40th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-79770?

CVE-2026-79770 is classified as CWE-1333 (CWE-1333). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-79770 published, and has it been updated?

CVE-2026-79770 was published on August 25, 2026 and was last updated on September 17, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎 RubyGems

Not in CISA KEV

CVE-2026-79770 — nokogiri

CVE-2026-79770 is a CWE-1333 vulnerability in nokogiri. A fix is available for nokogiri — see the affected versions and patch details below.

Nokogiri before 1.19.3 ReDoS via CSS selector tokenizer

Also known asGHSA-c4rq-3m3g-8wgx

Published

Aug 25, 2026

Updated

Sep 17, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-79770.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs40th percentile — riskier than 40% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

💎nokogiri

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

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

CWE-1333: Inefficient Regular Expression Complexity

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 Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`nokogiri`	all versions	1.19.3`bundle update nokogiri --conservative`

Affected Products

1 product · 1 configurations

Application

nokogirinokogiri

< 1.19.3

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nokogiri, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nokogiri to 1.19.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-79770 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

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…

Workaround published by Red Hat

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.

Source: Red Hat security advisory for CVE-2026-79770 (CC BY 4.0)

Frequently Asked Questions

## 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

O3 Security · Impact-Aware SCA

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