CVE-2026-72832: Grav Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-269c-h76q-8cxw",
  "modified" : "2026-09-17T17:28:34Z",
  "published" : "2026-09-17T17:28:34Z",
  "aliases" : [ "CVE-2026-72832" ],
  "summary" : "Grav: Stored XSS via quoted-attribute bypass in detectXss",
  "details" : "### Summary\n\nA page editor without `admin.super` can place an event handler after a `>` inside a quoted attribute. Grav accepts and stores the page, then executes the handler in the application origin when a visitor opens it.\n\n### Details\n\n`Security::detectXss()` (`system/src/Grav/Common/Security.php:253`) anchors the `on_events` scan at `<` and uses `[^>]*?`, which cannot cross the first literal `>`. When that character is inside a quoted value, the browser keeps the tag open and parses the later `onerror` attribute, so the detector and browser disagree. `AdminController::savePage()` relies on this detector when saving content from page editors outside the `admin.super` whitelist.\n\n### PoC\n\nI reproduced this with `getgrav/grav` 2.0.11 (`ad9709f865b09b68798fb1ac375b484a8cc1d892`), Admin 1.10.52, and Quark 2 1.1.4.\n\n1. Sign in as a user with `admin.login` and `admin.pages`, but without `admin.super`.\n2. Create or edit `/xsstest` and save this page body:\n\n```html\n<img src=x title=\">\" onerror=alert(document.domain)>\n```\n\n3. Open `/xsstest` in a private browser window.\n\nThe save succeeds and the visitor sees an alert containing the site domain. With the body changed to `<img src=x onerror=alert(1)>`, the same endpoint rejects it with `XSS issue detected` and does not store it.\n\n### Impact\n\nA page editor can execute JavaScript in the origin of every user who views the stored page, including unauthenticated visitors.\n\n### Anticipated objection and response\n\nAlthough the `detectXss()` docblock describes it as a heuristic that cannot catch every XSS, this check is the storage-time boundary for page editors outside the default `security.xss_whitelist` of `admin.super`. The same endpoint rejects a plain handler but accepts this executable form, allowing a lower-trust editor to cross the boundary the check is intended to enforce.\n\n### Suggested fix\n\nPrefer an HTML tokenizer or sanitizer that rejects event-handler attributes on parsed elements. If the existing tripwire remains, make its tag scan quote-aware instead of treating every `>` as a boundary. Add double-quoted and single-quoted regression cases plus the rejected plain-handler control.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "getgrav/grav"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.5.2"
      }, {
        "fixed" : "2.0.13"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.0.12"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/getgrav/grav/security/advisories/GHSA-269c-h76q-8cxw"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-72832"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/getgrav/grav/commit/ad9709f865b09b68798fb1ac375b484a8cc1d892"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/getgrav/grav"
  }, {
    "type" : "WEB",
    "url" : "https://www.vulncheck.com/advisories/grav-before-stored-xss-via-quoted-attribute-bypass"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-17T17:28:34Z",
    "nvd_published_at" : null
  }
}