GHSA-24X9-R6Q4-Q93W

Vulnerability from github – Published: 2026-05-21 21:25 – Updated: 2026-05-21 21:25
VLAI
Summary
Twig: `template_from_string()` escapes a SourcePolicy-driven sandbox via synthesized template name
Details

Description

When the sandbox is enabled selectively via SourcePolicyInterface (and not globally), a sandboxed template that is allowed to call template_from_string and include can render an arbitrary inner template with no security policy enforcement.

Environment::createTemplate() compiles the inner string under a synthesized name (__string_template__<hash>), so a name/path-based SourcePolicy returns false for it, and the inner template's checkSecurity() becomes a no-op. From a template the integrator believes is sandboxed, an attacker can use any tag/filter/function (including constant() to read secrets, or |map("system") to execute shell commands).

Resolution

This is a configuration trap rather than a code bug: there is no legitimate use case for exposing template_from_string to untrusted template authors, and propagating the parent sandbox state through template_from_string would require invasive changes to SourcePolicyInterface semantics with their own risks.

Starting with Twig 3.26.0, the documentation and the PHPDoc of StringLoaderExtension::templateFromString() explicitly warn against allowing template_from_string in a sandboxed environment (i.e. listing it in a SecurityPolicy allowed-functions list). Integrators using a SourcePolicyInterface MUST NOT allow template_from_string in their allowed functions; the safest option is not to register StringLoaderExtension at all when a sandbox is in use.

Credits

Twig would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue.

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "twig/twig"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.9.0"
            },
            {
              "fixed": "3.26.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-46634"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-693"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-21T21:25:12Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Description\n\nWhen the sandbox is enabled selectively via `SourcePolicyInterface` (and not globally), a sandboxed template that is allowed to call `template_from_string` and `include` can render an arbitrary inner template with no security policy enforcement.\n\n`Environment::createTemplate()` compiles the inner string under a synthesized name (`__string_template__\u003chash\u003e`), so a name/path-based `SourcePolicy` returns `false` for it, and the inner template\u0027s `checkSecurity()` becomes a no-op. From a template the integrator believes is sandboxed, an attacker can use any tag/filter/function (including `constant()` to read secrets, or `|map(\"system\")` to execute shell commands).\n\n### Resolution\n\nThis is a configuration trap rather than a code bug: there is no legitimate use case for exposing `template_from_string` to untrusted template authors, and propagating the parent sandbox state through `template_from_string` would require invasive changes to `SourcePolicyInterface` semantics with their own risks.\n\nStarting with Twig 3.26.0, the documentation and the PHPDoc of `StringLoaderExtension::templateFromString()` explicitly warn against allowing `template_from_string` in a sandboxed environment (i.e. listing it in a `SecurityPolicy` allowed-functions list). Integrators using a `SourcePolicyInterface` MUST NOT allow `template_from_string` in their allowed functions; the safest option is not to register `StringLoaderExtension` at all when a sandbox is in use.\n\n### Credits\n\nTwig would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue.",
  "id": "GHSA-24x9-r6q4-q93w",
  "modified": "2026-05-21T21:25:12Z",
  "published": "2026-05-21T21:25:12Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/twigphp/Twig/security/advisories/GHSA-24x9-r6q4-q93w"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FriendsOfPHP/security-advisories/blob/master/twig/twig/CVE-2026-46634.yaml"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/twigphp/Twig"
    },
    {
      "type": "WEB",
      "url": "https://symfony.com/cve-2026-46634"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [],
  "summary": "Twig: `template_from_string()` escapes a SourcePolicy-driven sandbox via synthesized template name"
}



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