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CVE-2026-45066 medium CVSS 6.1

Vulnerability in symfony/html-sanitizer (CVE-2026-45066)

Summary

Vulnerability in symfony/html-sanitizer (CVE-2026-45066). Risk of unauthorized operations or information disclosure. Exploitable via trusted.com. Mitigation: upgrade to 8.0.12 or later.

Original description

The description as published by the source.

Description

symfony/html-sanitizer lets applications sanitise untrusted HTML. The configuration methods allowLinkHosts([...]) and allowLinkSchemes([...]) are intended to restrict targets to an allowlist of hosts/schemes; `allowMediaHosts()` / `allowMediaSchemes()` do the same for etc.

Three distinct bypasses allow a content author to smuggle off-allowlist URLs past these checks. First, UrlSanitizer::parse() parses the input following RFC-3986, while browsers follow the WHATWG URL Standard which normalises \ to / before parsing the authority of "special" schemes; so an input like https://evil\@trusted.com/ parses with host trusted.com server-side but navigates to https://evil/ in the browser. Second, WHATWG collapses any run of / after the scheme into //, while RFC-3986 does not; so https:/evil.com/ and https:///evil.com/ parse as host-less (skipping the host allowlist) but resolve to evil.com in the browser. Third, UrlAttributeSanitizer checks 'a' === $element to route to the link policy and falls through to the media policy otherwise, but is a navigable hyperlink equivalent to; so `` was sanitised against the media policy (which typically allows data: and may have no host allowlist), bypassing allowLinkHosts() / allowLinkSchemes() entirely.

Resolution

UrlSanitizer::sanitize() now rejects URLs that contain a backslash or that use a special scheme (http, https, ftp, ws, wss) followed by a single slash or…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-45066 has been found in symfony/html-sanitizer.
Attackers can target a specific entry point like trusted.com over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 6.1/10.
What to do: upgrade symfony/html-sanitizer to 8.0.12 or later.
If unsure, ask your IT team or search "symfony/html-sanitizer CVE-2026-45066" on the vendor's site.

CVE-2026-45066 (symfony/html-sanitizer) — CWE-184 / CVSS v3 6.1
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: trusted.com / evil.com / UrlAttributeSanitizer / http
Patched: 8.0.12 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-184) exists in symfony/html-sanitizer. Attackers reach the vulnerable code path via trusted.com without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of symfony/html-sanitizer. Attack surface: trusted.com / evil.com / UrlAttributeSanitizer / http.

🔥 Severity

Severity: Medium (CVSS 6.1/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 8.0.12.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'symfony/html-sanitizer' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'symfony/html-sanitizer' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で symfony/html-sanitizer を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade symfony/html-sanitizer to 8.0.12

    ステージング環境で 8.0.12 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

composer symfony/html-sanitizer
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"8.0.12"}]}]
composer symfony/symfony
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"8.0.12"}]}]
Packagist symfony/html-sanitizer
[{"type":"ECOSYSTEM","events":[{"introduced":"8.0.0"},{"fixed":"8.0.12"}]}]
Packagist symfony/symfony
[{"type":"ECOSYSTEM","events":[{"introduced":"8.0.0"},{"fixed":"8.0.12"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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