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CVE-2026-49210 medium CVSS 6.1

Cross-Site Scripting (XSS) in symfony/ux-live-component (CVE-2026-49210)

Summary

Cross-site scripting in symfony/ux-live-component (CVE-2026-49210). Risk of unauthorized operations or information disclosure. Exploitable via LiveComponentSubscriber. Mitigation: upgrade to 3.1.0 or later.

Original description

The description as published by the source.

Description

Symfony\UX\LiveComponent\Util\ChildComponentPartialRenderer::createHtml() interpolates the $childTag argument directly into the HTML output as a tag name, without escaping or validation. The value originates from client-controlled JSON (children[id].tag) parsed by LiveComponentSubscriber and propagated through InterceptChildComponentRenderSubscriber, so an attacker who can reach the Live Component endpoint can inject arbitrary HTML, including `` tags, on any re-render of a Live Component that contains at least one child component.

In the default configuration, the Live Component endpoint is gated by an Accept: application/vnd.live-component+html request-header check that cannot be set cross-origin without a CORS preflight, so the issue is primarily a defense-in-depth gap. It becomes directly exploitable on applications that have relaxed CORS to allow this header from untrusted origins, or that have been pivoted from another same-origin XSS.

Resolution

ChildComponentPartialRenderer now validates $childTag against a strict HTML tag-name regex before interpolating it, and rejects any value that doesn't match. Anything that wouldn't be a valid HTML tag is dropped before reaching the response.

The patch for this issue is available here for branch 2.x (and forward-ported to 3.x).

Credits

Symfony would like to thank Pascal Cescon for reporting the issue and…

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-2026-49210 has been found in symfony/ux-live-component.
Attackers can target a specific entry point like LiveComponentSubscriber over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 6.1/10.
What to do: upgrade symfony/ux-live-component to 3.1.0 or later.
If unsure, ask your IT team or search "symfony/ux-live-component CVE-2026-49210" on the vendor's site.

CVE-2026-49210 (symfony/ux-live-component) — CWE-79 / CVSS v3 6.1
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: LiveComponentSubscriber / InterceptChildComponentRenderSubscriber / ChildComponentPartialRenderer
Patched: 3.1.0 — 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

Cross-site scripting (XSS) (CWE-79) exists in symfony/ux-live-component. Attackers reach the vulnerable code path via LiveComponentSubscriber without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of symfony/ux-live-component. Attack surface: LiveComponentSubscriber / InterceptChildComponentRenderSubscriber / ChildComponentPartialRenderer.

🔥 Severity

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

🔧 How to fix

Update to 3.1.0.

🛡️ 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/ux-live-component' . 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/ux-live-component' . | 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/ux-live-component 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/ux-live-component to 3.1.0

    ステージング環境で 3.1.0 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/ux-live-component
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.0"}]}]
Packagist symfony/ux-live-component
[{"type":"ECOSYSTEM","events":[{"introduced":"3.0.0"},{"fixed":"3.1.0"}]}]

References

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