Summary
svg-sanitizer Bypasses Attribute Sanitization
Problem
The sanitization logic at https://github.com/darylldoyle/svg-sanitizer/blob/0.21.0/src/Sanitizer.php#L454-L481 only searches for lower-case attribute names (e.g. xlink:href instead of xlink:HrEf), which allows to by-pass the isHrefSafeValue check. As a result this allows cross-site scripting or linking to external domains.
Proof-of-concept
provided by azizk
<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="100" height="100">
<a xlink:hReF="javascript:alert(document.domain)">
<rect width="100" height="50" fill="red"></rect>
<text x="50" y="30" text-anchor="middle" fill="white">Click me</text>
</a>
</svg>
Credits
The mentioned findings and proof-of-concept example were reported to the TYPO3 Security Team by the external security researcher azizk <[email protected]>.
Impact
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2025-55166? CVE-2025-55166 is a medium-severity cross-site scripting (XSS) vulnerability in enshrined/svg-sanitize (composer), affecting versions < 0.22.0. It is fixed in 0.22.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- Which versions of enshrined/svg-sanitize are affected by CVE-2025-55166? enshrined/svg-sanitize (composer) versions < 0.22.0 is affected.
- Is there a fix for CVE-2025-55166? Yes. CVE-2025-55166 is fixed in 0.22.0. Upgrade to this version or later.
- Is CVE-2025-55166 exploitable, and should I be worried? Whether CVE-2025-55166 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-55166 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2025-55166? Upgrade
enshrined/svg-sanitizeto 0.22.0 or later.