CVE-2026-121949
Description
A flaw was found in symfony/html-sanitizer. The HTML sanitizer fails to enforce configured media host and URL scheme restrictions on srcset and imagesrcset attributes. A remote attacker could exploit this vulnerability by submitting crafted HTML with image sources pointing to unauthorized domains. When another user views the sanitized content, their browser connects to the disallowed server, potentially allowing the attacker to track users or log their IP addresses.
Statement
This vulnerability is rated as Moderate severity because exploitation requires victim interaction and the resulting impact is confined to low-level information disclosure, such as client IP tracking, rather than arbitrary code execution or data corruption. In typical Red Hat environments, the Symfony HtmlSanitizer component is only exposed when applications explicitly define media domain or scheme restrictions while sanitizing untrusted markup. Without a user actively rendering the manipulated HTML output in a browser, the unverified image sources cannot trigger outbound network connections.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
Attackers may be able to find other malicious inputs that were not expected by the developer, allowing them to bypass the intended protection mechanism.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
