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🛡️ GHSA-c4rq-3m3g-8wgx — nokogiri

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-1333 OSV
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Nokogiri CSS selector tokenizer has regular expression backtracking

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.

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](https://cwe.mitre.org/data/definitions/1333.html)

Credit

Vector 1 was responsibly reported by @colby-swandale. Vectors 2 and 3 were discovered by @flavorjones during the response to the original report.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

GHSA-c4rq-3m3g-8wgx is classified as CWE-1333: Inefficient Regular Expression Complexity. A regular expression backtracks catastrophically on crafted input, consuming CPU out of proportion to input size.

Affected software

GHSA-c4rq-3m3g-8wgx is recorded against 1 package.

  • nokogiri (fixed in 1.19.3)

Timeline and source

Published on 6 May 2026 and last revised on 9 May 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

github.com (Web)
github.com (Package)

Other advisories for this package

nokogiri has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-1333: Inefficient Regular Expression Complexity) in other software:

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-1333
Public Exploit ✅ No
Source OSV
Published 2026-05-06
Updated 2026-08-20
Modified 2026-05-09
Fix URL N/A

Affected Packages

Software From version Fixed in
nokogiri — 1.19.3

Similar Threats

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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