Goal Reached Thanks to every supporter — we hit 100%!

Goal: 1000 CNY · Raised: 1359 CNY

100%
Buy Us a Coffee

CVE-2026-121949— Symfony: HtmlSanitizer Does Not URL-Sanitize srcset and imagesrcset: Media Scheme and Host Allow-List Bypass

Quick assessment

Affected
sensiolabs symfony
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Symfony 的 HtmlSanitizer 组件未对 和 属性应用媒体 URL 策略，导致指向未被 或 允许的主机或协议的值能够绕过该策略。因此，在 Symfony 6.1.x（6.4.50 之前）、7.x（7.4.23 之前）以及 8.x（8.1.11 之前）版本中，浏览器会从被禁止的主机加载图像。 具体而言， 和 元素上的 属性，以及 元素上的 属性，虽然被净化器允许通过，但其包含的 URL 候选值从未得到验证。因此，这些属性的值会被原样保留，而相同 URL 若出现在 属性中则会被丢弃。此前针对 CVE-2

CVSS 2.3 · Low

Affected Version Matrix 3

VendorProduct Version RangeStatus
sensiolabs symfony 6.1.0< 6.4.50 affected
7.0.0< 7.4.23 affected
8.0.0< 8.1.11 affected
Get alerts for future matching vulnerabilities Log in to subscribe

I. Basic Information for CVE-2026-121949

Vulnerability Information
Have questions about the vulnerability? See if Shenlong's analysis helps!
View Shenlong Deep Dive ↗

Although we use advanced large model technology, its output may still contain inaccurate or outdated information.Shenlong tries to ensure data accuracy, but please verify and judge based on the actual situation.

Vulnerability Title
Symfony: HtmlSanitizer Does Not URL-Sanitize srcset and imagesrcset: Media Scheme and Host Allow-List Bypass
Source: CVE Program / CVE List V5
Vulnerability Description
The Symfony HtmlSanitizer component does not apply the media URL policy to the srcset and imagesrcset attributes, allowing values that point to hosts or schemes not permitted by allowMediaSchemes() or allowMediaHosts() to bypass it, so that browsers load images from disallowed hosts in Symfony versions 6.1.x prior to 6.4.50, 7.x prior to 7.4.23, and 8.x prior to 8.1.11.The srcset attribute on img and source elements and the imagesrcset attribute on link elements are allowed by the sanitizer, but their URL candidates are never validated, so their values are kept verbatim while the same URL in src is dropped. The fixes for CVE-2026-45753 and CVE-2026-48761 extended the same attribute list but did not cover these two attributes. For example, with allowMediaSchemes(['https']) and allowMediaHosts(['trusted.example']), <img srcset="https://evil.example/a.png 1x"> survives sanitization, and the browser fetches the selected candidate as it would fetch src. Candidates with a scheme forbidden by the configuration, such as http, are kept as well. Any application that sanitizes untrusted HTML and relies on the media schemes and hosts allowlists to restrict where images can be loaded from is affected. A single crafted value is enough to make the browser of a user viewing the sanitized content send a request to an attacker-controlled host, which can be used to track viewers or log their IP addresses. No authentication is needed if the application accepts HTML from unauthenticated users.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
不完整的黑名单
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
sensiolabs symfony 6.1.0 ~ 6.4.50 -

II. Public POCs for CVE-2026-121949

# POC Description Source Link Shenlong Link
AI-Generated POC Premium

No public POC found.

Login to generate AI POC

III. Intelligence Information for CVE-2026-121949

请登录查看更多情报信息。

Other References for CVE-2026-121949 (2)

Same Patch Batch · sensiolabs · 2026-11-05 · 4 CVEs total

CVE-2026-123125 6.3 MEDIUM Symfony: Ip Constraint public/private Modes Accept IPv4-Mapped and IPv4-Compatible IPv6 Ad
CVE-2026-123119 2.3 LOW Symfony: NoPrivateNetworkHttpClient Does Not Pin the Checked IP of Cached Hosts, Letting D
CVE-2026-118517 2.3 LOW Symfony: HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URLs Without a Well

IV. Related Vulnerabilities

Same product: symfony
Same vendor: sensiolabs
Same weakness: CWE-184