CVE
Loofah regex-based denial of service in SVG reference check
- Exploited
- No known exploitation
- Fix
- Fixed in 2.25.3
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 2.25.3.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- FIRST's estimate of the chance attackers exploit it in the next 30 days, updated daily.What do these mean? →
- 0.40% · 35th percentile
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 32/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Loofah, a library for manipulating and transforming HTML and XML documents, has a flaw in the regular expression its HTML5 sanitizer uses to check SVG local references. A remote attacker who submits an SVG reference element with a long multiline-whitespace attribute can consume CPU during sanitization, causing a denial of service, without logging in or any action by a user.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Unknown: No advisory context yet
- Reach10/20Affects RubyGems packages
- Severity5.3/10CVSS 5.3
- No patch0/5No signal
What would change the score
- Would score about 77 if added to CISA KEV
- Would score about 72 if CISA's SSVC rates exploitation active
- Would score about 37 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 2.25.3.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-126205 (Loofah: Regular expression denial of service in the SVG local-reference check), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-126205 (entry last updated 2026-11-12):
Affected:
- flavorjones loofah: fixed in 2.25.3
- RubyGems package loofah: fixed in 2.25.3
Fixed versions: 2.25.3.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-126205 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126205 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Packages (RubyGems): find every lockfile in each project and run the stack.check operation of the cve.now MCP server (execute) on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/flavorjones/loofah/security/advisories/GHSA-mf2j-8f84-cc9q
- https://github.com/flavorjones/loofah/pull/324
- https://github.com/flavorjones/loofah/commit/2f31e7fae36036c9882d3d0fae720e1014c57cd1
- https://github.com/flavorjones/loofah/releases/tag/v2.25.3
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.
Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.
Entry: https://cve.now/CVE-2026-126205
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-126205"}.Timeline
- CVE published
- First seen by cve.now
Affected versions
- flavorjones loofah
fixed in 2.25.3
- loofahRubyGems
fixed in 2.25.3
Evidence 6
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 3
- Repository
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-126205
Is CVE-2026-126205 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-126205?
loofah: before 2.25.3. loofah (RubyGems): before 2.25.3.Source: cve.now feed data
How do I fix CVE-2026-126205?
Upgrade to a fixed version: 2.25.3.Source: cve.now feed data