Security Flaw in Symfony HtmlSanitizer Component Affects Multiple Versions
CVE-2026-121949

2.3LOW

Key Information:

Vendor

Sensiolabs

Status
Symfony
Vendor
CVE Published:
5 November 2026

What is CVE-2026-121949?

The Symfony HtmlSanitizer component contains a vulnerability that allows the srcset and imagesrcset attributes to bypass media URL policies. This oversight enables malicious URLs from untrusted hosts to be processed without validation, allowing harmful content to load in a user's browser. No authentication is required, putting users at risk of tracking or data exposure from untrusted sources. Developers relying on this sanitization for HTML input need to be aware of this issue, as crafted inputs can easily exploit this weakness and compromise user privacy.

Affected Version(s)

symfony 6.1.0 < 6.4.50

symfony 7.0.0 < 7.4.23

symfony 8.0.0 < 8.1.11

References

https://github.com/symfony/symfony/security/advisories/GH...
third-party-advisory
https://github.com/symfony/symfony/commit/50e7a38a8f08860...
patch

CVSS V4

Score:
2.3
Severity:
LOW
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
Physical
Privileges Required:
Undefined
User Interaction:
Unknown

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Shriyansh Gupta
Ilia Alshanetsky
李智遥
Nicolas Grekas
.