Smarty Security stream restriction bypass through stream: resource

NVD Description

`smarty/smarty` version `5.8.0` can read local files through PHP stream wrappers even when Smarty Security is enabled and all streams are disabled with `Security::$streams = null`. The bypass uses Smarty's built-in `stream:` resource type. A template such as: ```smarty {include file="stream:php://filter/read=convert.base64-encode/resource=/tmp/secret.tpl"} ``` is handled as Smarty resource type `stream`, so the security check that would normally reject the underlying `php` wrapper is not applied. `StreamPlugin` then opens the nested `php://filter/...` URI directly. For comparison, the direct resource: ```smarty {include file="php://filter/read=convert.base64-encode/resource=/tmp/secret.tpl"} ``` is blocked with `stream 'php' not allowed by security setting`. Affected package: - Ecosystem: Packagist / Composer - Package: `smarty/smarty` - Confirmed affected version: `5.8.0` - Confirmed source reference from Composer lock: `78d259d3b971c59a0cd719c270cc5cbb740c36a7` - Current stable version on Packagist at review time: `v5.8.0` - Packagist usage at review time: 41,113,855 total downloads and 840,604 monthly downloads Relevant code paths: - `Smarty\Resource\BasePlugin::load(...)` - `Smarty\Resource\StreamPlugin::getContent(...)` - `Smarty\Security::isTrustedStream(...)` `BasePlugin::load()` maps the built-in resource name `stream` directly to `StreamPlugin` before the code path that checks PHP stream wrappers with `stream_get_wrappers()` and `Security::isTrustedStream($type)`. `StreamPlugin::getContent()` later calls `fopen($filepath, 'r+')` on the nested URI when the resource name contains `://`. Preconditions: An application must render templates that are not fully trusted while relying on Smarty Security to restrict local files and PHP stream wrappers. The PoC sets: ```php $smarty->enableSecurity(); $smarty->security_policy->streams = null; ``` Local reproduction: The PoC creates a disposable template directory and a separate outside directory. It enables Smarty Security, disables all streams, and then compares three includes: 1. `../outside/secret.tpl` to confirm the ordinary trusted-directory boundary is enforced. 2. `php://filter/...` to confirm direct PHP streams are blocked by `Security::$streams = null`. 3. `stream:php://filter/...` to show the built-in `stream:` resource bypasses the same restriction and reads the outside file. Run: ```shell php -d display_errors=1 poc.php ``` Observed sanitized output: ```text package=smarty/smarty installed_version=v5.8.0 template_dir=<tmp>/templates outside_template=<tmp>/outside/secret.tpl plain_dotdot_include=BLOCKED:Smarty\Exception:Smarty Security: not trusted file path '<tmp>/outside/secret.tpl' direct_php_filter_include=BLOCKED:Smarty\Exception:stream 'php' not allowed by security setting stream_php_filter_include=OK:U01BUlRZX1NUUkVBTV9XUkFQUEVSX1NFQ1VSSVRZX0VTQ0FQRQ== expected_base64=U01BUlRZX1NUUkVBTV9XUkFQUEVSX1NFQ1VSSVRZX0VTQ0FQRQ== ``` The `plain_dotdot_include` line shows the directory boundary is enforced for ordinary traversal. The `direct_php_filter_include` line shows the same policy rejects `php://filter` when used directly. The `stream_php_filter_include` line shows that wrapping the same URI in Smarty's `stream:` resource bypasses that restriction and reads the outside file. Impact: A template author can bypass Smarty Security stream restrictions and read local files that are readable by the PHP process. With `php://filter`, file contents can be base64 encoded and rendered back through the template. This bypasses both the intended `Security::$streams = null` restriction and the normal trusted-template-directory check that blocks `../` traversal. Duplicate checks: - OSV query for `Packagist/smarty/smarty` version `5.8.0` returned no vulnerabilities. - GitHub advisory query for `ecosystem=composer` and `affects=smarty/smarty` returned historical Smarty advisories, including sandbox escapes, PHP code injection, XSS, and older path traversal issues. The listed path traversal advisories affect older versions and do not describe this current `stream:php://filter` resource-wrapper bypass in 5.8.0. - GitHub issue search in `smarty-php/smarty` for `stream:php://filter` returned zero results. - Public searches for `Smarty StreamPlugin php://filter` and `smarty/smarty isTrustedStream stream:` did not identify a clear public duplicate during triage. Suggested remediation: When resolving the built-in `stream:` resource, parse and validate the nested URI scheme before opening it. For example, `stream:php://filter/...` should call `Security::isTrustedStream('php')`, and `Security::$streams = null` should block the resource before `StreamPlugin::getContent()` reaches `fopen()`. It would also be safer for `StreamPlugin` to reject nested stream wrappers by default unless the underlying wrapper is explicitly allowed by the active security policy.

Affected Packages (1)