GHSA-24X9-R6Q4-Q93W
Vulnerability from github – Published: 2026-05-21 21:25 – Updated: 2026-05-21 21:25Description
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.
{
"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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