CVE-2026-47732: Twig Sandbox: Multiple `__toString()` Policy Bypasses Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-pr2w-4gpj-cpq4",
  "modified" : "2026-06-05T21:47:11Z",
  "published" : "2026-06-05T21:47:11Z",
  "aliases" : [ "CVE-2026-47732" ],
  "summary" : "Twig: Sandbox: multiple `__toString()` policy bypasses via unguarded string coercion points",
  "details" : "### Description\n\n`SandboxNodeVisitor` enforces `SecurityPolicy::checkMethodAllowed()` for implicit `__toString()` calls by wrapping selected AST nodes in `CheckToStringNode`. The set of wrapped nodes is incomplete, and several Twig language constructs still trigger PHP string coercion on a `Stringable` operand without first consulting the policy. A sandboxed template author can therefore invoke `__toString()` on any object reachable in the render context, even when `__toString` on its class is not allowlisted.\n\nConfirmed bypass vectors:\n\n- Conditional expressions (`a ? b : c`, `a ?: b`, `a ?? b`) used as the input of a string-coercing filter or as a filter/function argument.\n- The `matches` operator and the loose comparison operators (`==`, `!=`, `<`, `>`, `<=`, `>=`, `<=>`), which coerce a `Stringable` operand to string and can be used as an oracle to recover the value byte by byte (no tag, filter or function needs to be allowlisted).\n- Twig tests in general (which were never policy-gated), in particular `is empty` which casts a `Stringable` value via `(string) $value` in `CoreExtension::testEmpty()`.\n- Null-coalesce expressions nested in concatenation, and the direct output of allowed functions or filters that return a `Stringable` object.\n- Arguments passed to allowed object methods, template-name expressions of template-loading tags (`include`, `extends`, `use`, ...), dynamic attribute/property names, and spread arguments from `Traversable` objects.\n- The `do` tag and the `..` range operator.\n\n### Resolution\n\nThe sandbox now wraps every child node that the parent will string-coerce at runtime, instead of relying on a hardcoded list of node types in `SandboxNodeVisitor`. A new `Twig\\Node\\CoercesChildrenToStringInterface` lets nodes declare which of their children must be guarded; core nodes (concatenation, comparison and range binaries, filter/function/test expressions, `do`, `include`, `extends`, `use`, ...) implement it. Spread arguments are materialised and policy-checked via the new `SandboxExtension::ensureSpreadAllowed()`, and dynamic attribute names are checked at runtime inside `CoreExtension::getAttribute()`.\n\n### Credits\n\nTwig would like to thank Anthropic Glasswing and El Kharoubi Iosif for reporting the issues, and Fabien Potencier for providing the fixes.",
  "severity" : [ ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "twig/twig"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.26.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.25.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/twigphp/Twig/security/advisories/GHSA-pr2w-4gpj-cpq4"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/FriendsOfPHP/security-advisories/blob/master/twig/twig/CVE-2026-47732.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/twigphp/Twig"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/twigphp/Twig/releases/tag/v3.26.0"
  }, {
    "type" : "WEB",
    "url" : "https://symfony.com/cve-2026-47732"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-05T21:47:11Z",
    "nvd_published_at" : null
  }
}