ghsa-pq4g-8rxf-4g29

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "<= 1.0.7",
        "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-pq4g-8rxf-4g29/GHSA-pq4g-8rxf-4g29.json"
      },
      "package": {
        "ecosystem": "RubyGems",
        "name": "crass",
        "purl": "pkg:gem/crass"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.0.8"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.0.1",
        "0.0.2",
        "0.1.0",
        "0.2.0",
        "0.2.1",
        "1.0.0",
        "1.0.1",
        "1.0.2",
        "1.0.3",
        "1.0.4",
        "1.0.5",
        "1.0.6",
        "1.0.7"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-116695"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-436"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-28T22:42:53Z",
    "nvd_published_at": "2026-10-27T21:18:05Z",
    "severity": "MODERATE"
  },
  "details": "## Summary\n\nCrass's tokenizer didn't terminate a bad URL token at a `)` that followed an escaped backslash (`\\\\`). As a result, Crass consumed more input as part of the bad URL than a spec-compliant browser does. CSS sanitizers that parse untrusted CSS with Crass and re-emit it could be tricked into passing through declarations, style rules, or at-rules (including `@import`) that the sanitizer would otherwise have removed, but that a browser would then parse and apply.\n\n## Details\n\nWhile consuming the remnants of a bad URL (CSS Syntax Level 3, §4.3.15), Crass checked whether the *previously consumed* code point and the next code point formed a valid escape, in addition to checking the next two unconsumed code points. After an escaped backslash, the previously consumed code point is a backslash, so a following `)` was incorrectly treated as escaped and the bad URL token continued until the next unescaped `)` or the end of the input.\n\nBrowsers terminate the bad URL at that `)`, so everything Crass treated as part of the bad URL is live CSS to a browser.\n\nThis bug has existed in every released version of Crass.\n\n## Impact\n\nCrass by itself only mis-tokenizes input. The security impact is on CSS sanitizers that use Crass to make allow/deny decisions and then re-serialize the CSS. Exploitation requires a sanitizer that doesn't reject bad URL tokens wherever they occur. Confirmed examples (verified in Chromium against the sanitizers' output):\n\n- **Sanitize** (all versions through 7.0.0):\n  - In `Sanitize::CSS.properties` and `style` attributes, a bad URL inside a `[...]` or `(...)` block in the value of an allowlisted property can smuggle arbitrary declarations, such as `position: fixed` or a `background-image` URL with a disallowed protocol.\n  - In `Sanitize::CSS.stylesheet` and `<style>` elements, a bad URL in a selector can smuggle arbitrary style rules and at-rules, including `@import`.\n- **Loofah** (`Loofah::HTML5::Scrub.scrub_css`, used for `style` attributes), and therefore **rails-html-sanitizer** (`sanitize_css`, and `sanitize` when `style` is a permitted attribute): a bad URL inside an allowlisted function such as `calc()` or `rgb()` can smuggle declarations Loofah normally strips, such as `position: fixed` and `url()` values.\n\nSmuggled CSS can be used for UI redress (clickjacking or phishing overlays), loading attacker-controlled external resources, and, where rules or `@import` can be smuggled, CSS-based data exfiltration. This vulnerability doesn't allow script execution in modern browsers.\n\n## Patches\n\nFixed in Crass 1.0.8. Users of Sanitize, Loofah, rails-html-sanitizer, or any other library that uses Crass to sanitize CSS should upgrade Crass to 1.0.8 or later.\n\n## Workarounds\n\nThere are no practical workarounds other than upgrading. Rejecting any CSS input that contains the character sequence `\\\\` would block the known trigger, but this is a blunt measure and may reject legitimate CSS.\n\n## References\n\n- CSS Syntax Module Level 3, \"Consume the remnants of a bad url\": https://drafts.csswg.org/css-syntax-3/#consume-remnants-of-bad-url",
  "id": "GHSA-pq4g-8rxf-4g29",
  "modified": "2026-10-28T23:00:04.150123033Z",
  "published": "2026-10-28T22:42:53Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/rgrove/crass/security/advisories/GHSA-pq4g-8rxf-4g29"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-116695"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rgrove/crass/commit/689fc45c632fdf3803b2f4e844ffc9cca3b08f34"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/rgrove/crass"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rgrove/crass/releases/tag/v1.0.8"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/crass/GHSA-pq4g-8rxf-4g29.yml"
    }
  ],
  "schema_version": "1.9.2",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Crass: Incorrect tokenization of bad URLs enables CSS sanitizer bypass"
}