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CVE-2026-118517— Symfony: HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URLs Without a Well-Formed Authority (Incomplete Fix for CVE-2026-45066)

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 组件中的 UrlSanitizer 在解析 URL 时与浏览器的行为不一致，导致对于缺少规范权威部分（authority）的 URL， 和 的校验机制可能被绕过。这使得不受信任的主机能够出现在经过清洗的输出中。该漏洞影响 Symfony 6.1.x 系列（6.4.50 之前版本）、7.x 系列（7.4.23 之前版本）以及 8.x 系列（8.1.11 之前版本）。 UrlSanitizer 使用 库来解析 URL，该库遵循 RFC 3986 标准，而浏览器则遵循 WH

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
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I. Basic Information for CVE-2026-118517

Vulnerability Information
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Vulnerability Title
Symfony: HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URLs Without a Well-Formed Authority (Incomplete Fix for CVE-2026-45066)
Source: CVE Program / CVE List V5
Vulnerability Description
The Symfony HtmlSanitizer component UrlSanitizer parses URLs differently from browsers, allowing the allowLinkHosts() and allowMediaHosts() checks to be bypassed for URLs without a well-formed authority, resulting in untrusted hosts being referenced in sanitized output 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. UrlSanitizer parses URLs with league/uri, which follows RFC 3986, while browsers follow the WHATWG URL standard. For URLs without a well-formed authority, such as http:evil.example, ///evil.example, or https://://evil.example/ the sanitizer finds no host, whereas browsers resolve them to evil.example. The guard added for CVE-2026-45066 missed the zero-slash form, and the host 0 was also skipped because PHP treats it as falsy. This is exploitable when a host allow-list is combined with allowRelativeLinks(true) or allowRelativeMedias(true). The default configuration is not affected.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/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-2026-118517

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III. Intelligence Information for CVE-2026-118517

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Other References for CVE-2026-118517 (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-2026-121949 2.3 LOW Symfony: HtmlSanitizer Does Not URL-Sanitize srcset and imagesrcset: Media Scheme and Host

IV. Related Vulnerabilities

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