CVE-2026-126205 Loofah: Regular expression denial of service in the SVG local-reference check
Attackers can submit SVG references with long whitespace to cause quadratic CPU use in Loofah sanitization; Ruby apps using Loofah should care.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Harmful if only installed
- No
- Needs a specific call
- No
- Fix
- Available
What is CVE-2026-126205?
CVE-2026-126205 is a medium-severity denial of service vulnerability in flavorjones loofah, published on 12 Nov 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-126205?
1 open source package ship an affected version, including loofah.
An affected version is exposed as installed. No special setting or call is needed.
| Package | Affected | Fixed in |
|---|---|---|
loofah RubyGems | All versions | 2.25.3 |
How do I fix CVE-2026-126205?
Upgrade loofah to 2.25.3 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-126205 being exploited?
There is no known exploitation of CVE-2026-126205 in the wild and no public exploit code.
Sources
Also known as GHSA-mf2j-8f84-cc9q.