This commmit adds the runtime options
- `allowProtoPropertiesByDefault` (boolean, default: false) and
- `allowProtoMethodsByDefault` (boolean, default: false)`
which can be used to allow access to prototype properties and
functions in general.
Specific properties and methods can still be disabled from access
via `allowedProtoProperties` and `allowedProtoMethods` by
setting the corresponding values to false.
The methods `constructor`, `__defineGetter__`, `__defineSetter__`, `__lookupGetter__`
and the property `__proto__` will be disabled, even if the allow...ByDefault-options
are set to true. In order to allow access to those properties and methods, they have
to be explicitly set to true in the 'allowedProto...'-options.
A warning is logged when the a proto-access it attempted and denied
by default (i.e. if no option is set by the user to make the access
decision explicit)
Disallow access to prototype properties and methods by default.
Access to properties is always checked via
`Object.prototype.hasOwnProperty.call(parent, propertyName)`.
New runtime options:
- **allowedProtoMethods**: a string-to-boolean map of property-names that are allowed if they are methods of the parent object.
- **allowedProtoProperties**: a string-to-boolean map of property-names that are allowed if they are properties but not methods of the parent object.
```js
const template = handlebars.compile('{{aString.trim}}')
const result = template({ aString: ' abc ' })
// result is empty, because trim is defined at String prototype
```
```js
const template = handlebars.compile('{{aString.trim}}')
const result = template({ aString: ' abc ' }, {
allowedProtoMethods: {
trim: true
}
})
// result = 'abc'
```
Implementation details: The method now "container.lookupProperty"
handles the prototype-checks and the white-lists. It is used in
- JavaScriptCompiler#nameLookup
- The "lookup"-helper (passed to all helpers as "options.lookupProperty")
- The "lookup" function at the container, which is used for recursive lookups in "compat" mode
Compatibility:
- **Old precompiled templates work with new runtimes**: The "options.lookupPropery"-function is passed to the helper by a wrapper, not by the compiled templated.
- **New templates work with old runtimes**: The template contains a function that is used as fallback if the "lookupProperty"-function cannot be found at the container. However, the runtime-options "allowedProtoProperties" and "allowedProtoMethods" only work with the newest runtime.
BREAKING CHANGE:
- access to prototype properties is forbidden completely by default
- context.propertyIsEnumerable can be replaced
via __definedGetter__
- This is a fix specific to counter a known RCE exploit.
Other fixes will follow.
closes#1563
- The "lookup" helper could also be used to run a remote code execution
by manipulating the template. The same check as for regular
path queries now also is done in the "lookup"-helper
This commit fixes a Remote Code Execution (RCE) reported by
npm-security. Access to non-enumerable "constructor"-properties
is now prohibited by the compiled template-code, because this
the first step on the way to creating and execution arbitrary
JavaScript code.
The vulnerability affects systems where an attacker is allowed to
inject templates into the Handlebars setup.
Further details of the attack may be disclosed by npm-security.
Closes#1267Closes#1495
Jakob Linskeseder
Nils Knappmeier
John Boehr
Nils Knappmeier