Twig is a template language for PHP. Prior to 3.27.0, the sandbox __toString() checks do not fully cover Traversable values passed to join and replace filters or operands evaluated by the in and not in operators, allowing contained Stringable objects to be coerced to strings without consulting the sandbox policy. This issue is fixed in version 3.27.0.

Affected: Packagist: twig/twig

### Description

This is a residual bypass of CVE-2026-47732 / GHSA-pr2w-4gpj-cpq4 left after the initial fix for unguarded `__toString()` calls. It covers two related coercion points that were not caught by the original patch.

**`Traversable` in `join` and `replace` filters.** `SandboxExtension::ensureToStringAllowed()` recurses into PHP arrays so that a `Stringable` object hidden inside an array argument cannot be string-coerced without consulting the security policy. The recursion stops at PHP arrays: a `Traversable` value passed at the same position is not materialised, so its contents are not policy-checked. `CoreExtension::join()` and `CoreExtension::replace()` later materialise such `Traversable` inputs through `self::toArray()` and feed them to `implode()` / `strtr()`, both of which implicitly call `__toString()` on contained `Stringable` objects. The bypass also reproduces when the container implements both `Stringable` and `Traversable`: the container's own `__toString()` is policy-checked, but the elements yielded by `getIterator()` are not, and the consuming filters still coerce them to string.

**`in` and `not in` operators.** `InBinary` and `NotInBinary` compile to `CoreExtension::inFilter()`, which falls through to PHP's `<=>` operator when comparing a string with a `Stringable` object. PHP coerces the object to string via `__toString()` without the sandbox policy being consulted. Beyond the direct side effect, `in` can also be used as a content-leak oracle:…

Affected: Ubuntu:Pro:20.04:LTS: php-twig, Ubuntu:Pro:22.04:LTS: php-twig, Ubuntu:Pro:24.04:LTS: php-twig, Ubuntu:25.10: php-twig, Ubuntu:Pro:26.04:LTS: php-twig

Twig is a template language for PHP. Prior to 3.27.0, the sandbox __toString() checks do not fully cover Traversable values passed to join and replace filters or operands evaluated by the in and not in operators, allowing contained Stringable objects to be coerced to strings without consulting the sandbox policy. This issue is fixed in version 3.27.0.