GHSA-6V8J-33HC-MV84

Vulnerability from github – Published: 2026-06-19 21:42 – Updated: 2026-06-19 21:42
VLAI
Summary
symfony/ux-icons: XSS via unsanitized SVG content in local files and Iconify on-demand responses
Details

Description

The ux_icon() Twig function is marked is_safe=['html'], so Twig never escapes its output. Icon::toHtml() inlines the SVG source verbatim into the page. Browsers execute <script> elements and on* event-handler attributes found inside inline SVG, making any unsanitized icon a vector for cross-site scripting.

Two code paths were affected. In the local file path, Icon::fromFile() only stripped <script> elements that were direct children of <svg>, leaving nested scripts and all on* attributes untouched despite a code comment claiming broader protection. In the Iconify on-demand path (enabled by default), the remote JSON body field was wrapped into an Icon object with no sanitization at all. Concrete attack vectors include a malicious SVG icon pack from a third-party theme or downloaded icon set, or a controlled Iconify endpoint configured via iconify.endpoint (including a poisoned cache).

Resolution

Introducing an IconFactory that centralizes sanitization across every icon source before an Icon object is created. The sanitizer removes script-capable elements (script, foreignObject, iframe, object, embed), SMIL animations targeting on*, href, or xlink:href attributes, CDATA sections, processing instructions, all on* attributes, and javascript:, vbscript:, and data:text/html URL schemes. <style> elements are kept for theming but have any handlers stripped. Icons that contain none of these constructs are byte-for-byte identical after sanitization.

Credits

Symfony would like to thank Pascal Cescon for reporting the issue and Hugo Alliaume for providing the fix.

Severity
6.1 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "symfony/ux-icons"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.17.0"
            },
            {
              "fixed": "2.36.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "symfony/ux-icons"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "3.2.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55877"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T21:42:15Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Description\n\nThe `ux_icon()` Twig function is marked `is_safe=[\u0027html\u0027]`, so Twig never escapes its output. `Icon::toHtml()` inlines the SVG source verbatim into the page. Browsers execute `\u003cscript\u003e` elements and `on*` event-handler attributes found inside inline SVG, making any unsanitized icon a vector for cross-site scripting.\n\nTwo code paths were affected. In the local file path, `Icon::fromFile()` only stripped `\u003cscript\u003e` elements that were direct children of `\u003csvg\u003e`, leaving nested scripts and all `on*` attributes untouched despite a code comment claiming broader protection. In the Iconify on-demand path (enabled by default), the remote JSON `body` field was wrapped into an `Icon` object with no sanitization at all. Concrete attack vectors include a malicious SVG icon pack from a third-party theme or downloaded icon set, or a controlled Iconify endpoint configured via `iconify.endpoint` (including a poisoned cache).\n\n### Resolution\n\nIntroducing an `IconFactory` that centralizes sanitization across every icon source before an `Icon` object is created. The sanitizer removes script-capable elements (`script`, `foreignObject`, `iframe`, `object`, `embed`), SMIL animations targeting `on*`, `href`, or `xlink:href` attributes, CDATA sections, processing instructions, all `on*` attributes, and `javascript:`, `vbscript:`, and `data:text/html` URL schemes. \n`\u003cstyle\u003e` elements are kept for theming but have any handlers stripped. Icons that contain none of these constructs are byte-for-byte identical after sanitization. \n\n### Credits\n\nSymfony would like to thank Pascal Cescon for reporting the issue and Hugo Alliaume for providing the fix.",
  "id": "GHSA-6v8j-33hc-mv84",
  "modified": "2026-06-19T21:42:15Z",
  "published": "2026-06-19T21:42:15Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/symfony/ux/security/advisories/GHSA-6v8j-33hc-mv84"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/ux-icons/CVE-2026-55877.yaml"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/symfony/ux"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "symfony/ux-icons: XSS via unsanitized SVG content in local files and Iconify on-demand responses"
}



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