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MEDIUM severity

CVE-2026-126205 — Flavorjones

MEDIUMFix: flavorjones/loofah@2f31e7f

CVE-2026-126205 is a medium-severity (CVSS 5.3) Uncontrolled Resource Consumption vulnerability. The records list no fixed version yet; check the vendor advisory below and apply the mitigations in the meantime.

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. Prior to 2.25.3, the Loofah HTML5 sanitizer checks href and…

Published
Updated
Affected
—
Patched
See advisory
Exploits
None indexed
Exploitation data as of Nov 12, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Description

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. Prior to 2.25.3, the Loofah HTML5 sanitizer checks href and xlink:href on elements in SVG_ALLOW_LOCAL_HREF with a regular expression whose line anchor and newline-matching whitespace cause an all-whitespace value to be rescanned from every line start. An attacker can submit an SVG reference element with a long multiline-whitespace attribute and consume CPU quadratically during sanitization. CRuby 3.1 and earlier and JRuby are affected, while CRuby 3.2 and later uses linear-time regular-expression matching. The default safelist reaches the vulnerable check without a configuration change. This issue is fixed in version 2.25.3.

Detection & mitigation playbook

Vulnerability

  1. Detect

    Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).

  2. Remediation status

    The records we use list no fixed release for CVE-2026-126205. Check the upstream advisory for a patched version, and apply the exposure-reduction steps below in the meantime.

  3. Mitigate without a patch

    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.

Frequently Asked Questions

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. Prior to 2.25.3, the Loofah HTML5 sanitizer checks href and xlink:href on elements in SVG_ALLOW_LOCAL_HREF with a regular expression whose line anchor and newline-matching whitespace cause an all-whitespace value to be rescanned from every line start. An attacker can submit an SVG reference element with a long multiline-whitespace attribute and consume CPU quadratically during sanitization. CRuby 3.1 and earlier and JRuby are affected, while CRuby 3.2 and later uses linear-
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CVE-2026-126205: Flavorjones (Medium 5.3)