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GHSA-mf2j-8f84-cc9q

Loofah: Regular expression denial of service in the SVG local-reference check

Products / packages flavorjones loofah · loofah

Published

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Severity and exploitation

Not in CISA KEVSource: MODERATE

KEV coverage does not rule out exploitation.

KEV checked 15/11/2026, 03:00:33 UTC
OSV · CVSS:3.1 · 5.3
Assessment vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
GitHub_M · CVSS:3.1 · 5.3
Assessment vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
The headline uses the highest imported catalog score. Assessments can differ by source and CVSS version.

Severity

medium5.3

CVSS measures technical severity, not the likelihood of an attack.

Known exploitation

Not listed in the checked CISA KEV catalog

Absence from CISA KEV does not rule out attacks.

Public exploit

Not established by this record

Missing evidence does not mean no public exploit exists.

Remediation

Package fixes recorded

Fix versions are recorded for 1 of 1 mapped packages. Check each release branch and any separate product guidance.

What this means

Loofah's HTML5 sanitizer restricts the href and xlink:href attributes of SVG reference elements to local references. That check matched the attribute value against /^\s[^\s]./m. In Ruby ^ anchors to every line start and \s matches newlines, so an all-whitespace value made the engine rescan the value from each of its line starts, taking time quadratic in its length.

Source excerpt · OSV

Attack conditions

No attack-condition excerpt has been identified here. Review the full source description and references for authentication, network access, and configuration requirements.

Review supporting sources →

Affected versions

Check the exact model, release, and any platform requirements against your installation.

flavorjones · GitHub_M

loofah

1 range
GitHub_M version evidence

Compare with this publisher’s ranges. This does not inspect your installation.

affected

< 2.25.3

unaffected

unknown

Other versions: unknown

Packages

Compare each installed version with the publisher’s affected ranges. Where a fix is recorded, choose the appropriate release branch and test compatibility before upgrading.

loofah RubyGems
Affected range Recorded fix
Earlier releases before 2.25.3Ecosystem versions2.25.3

Version evidence: OSV · GHSA-mf2j-8f84-cc9q

View original version evidence (65 explicit versions)

What to do

Compare your installed product and version with the affected versions above. A matching product name alone does not confirm exposure.

Use the recorded fix for your release branch. Review the publisher’s instructions and test compatibility before upgrading.

cve.new guidance unless attributed to a publisher. This page does not inspect your installation.

Public exploit evidence

No public exploit reference is identified in the imported evidence. This is not a claim that no exploit exists.

Original source description

Read the full publisher description

Summary

Loofah's HTML5 sanitizer restricts the href and xlink:href attributes of SVG reference elements to local references. That check matched the attribute value against /^\s*[^#\s].*/m. In Ruby ^ anchors to every line start and \s matches newlines, so an all-whitespace value made the engine rescan the value from each of its line starts, taking time quadratic in its length.

Only Ruby 3.1 and earlier are affected. Ruby 3.2 added linear-time regexp matching, which makes the pattern linear.

Impact

An attacker who supplies HTML to be sanitized can consume CPU out of proportion to the input size, by sending an SVG reference element whose href or xlink:href is a long run of whitespace.

The default safelist allows the elements in SVG_ALLOW_LOCAL_HREF, so no configuration change is required.

Mitigation

Upgrade to Loofah >= 2.25.3. Applications that cannot upgrade should run Ruby 3.2 or later, which matches the pattern in linear time.

Credit

Reported by scyoon through the Rails HackerOne program.

References

6 sources
flavorjones/loofah · security/advisories/GHSA-mf2j-8f84-cc9q
Security advisoryGitHub_M
flavorjones/loofah · pull request #324
PatchGitHub_M
flavorjones/loofah · commit 2f31e7f
PatchGitHub_M
flavorjones/loofah · repository
Source reference
flavorjones/loofah · releases/tag/v2.25.3
Release notesGitHub_M
rubysec/ruby-advisory-db · GHSA-mf2j-8f84-cc9q.yml
Source reference

Inside the record

Evidence available

Package identity
Version evidence
Remediation guidance · not supplied
Weakness classification
Additional publishers · not supplied

Describes the evidence in this view, not whether the product is safe.

Original records

CVE-2026-126205

View the latest unmodified CVE JSON from the official source. It may be newer than this imported page.

cve.new JSON →

Underlying weaknesses

The source’s classification of what caused the vulnerability.

CWE-400 ↗

CWE-400: Uncontrolled Resource Consumption

GitHub_M

Related →
CWE-1333 ↗

CWE-1333: Inefficient Regular Expression Complexity

GitHub_M

Related →
Contributing organizations · 1
GitHub_M

Assigning organization

2026-11-12

Timeline

All times UTC

  1. Advisory published

    Publication date supplied by the source.

  2. Source updated

    Latest modification date supplied by the source.

  3. Last imported by cve.new

    Latest catalog import, not the date we first saw this advisory.

What changed

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