CVE-2021-21316

### Impact When processing theming resources (i.e. `*.less` files) with less-openui5 that originate from an untrusted source, those resources might contain JavaScript code which will be executed in the context of the build process. While this is a [feature](http://lesscss.org/usage/#less-options-enable-inline-javascript-deprecated-) of the [Less.js library](https://github.com/less/less.js), it is an unexpected behavior in the context of OpenUI5 and SAPUI5 development. Especially in the context of [UI5 Tooling](https://github.com/SAP/ui5-tooling), which relies on less-openui5, this poses a security threat: An attacker might create a [library](https://sap.github.io/ui5-tooling/pages/Builder/#library) or [theme-library](https://sap.github.io/ui5-tooling/pages/Builder/#theme-library) containing a custom control or theme, hiding malicious JavaScript code in one of the `.less` files. This is an example of inline JavaScript in a Less file: ```less .rule { @var: `(function(){console.log('Hello from JavaScript'); process.exit(1);})()`; color: @var; } ``` Starting with Less.js version 3.0.0, the Inline JavaScript feature is disabled by default. less-openui5 however currently uses [a fork](https://github.com/SAP/less-openui5/tree/master/lib/thirdparty/less) of Less.js v1.6.3. Note that disabling the Inline JavaScript feature in Less.js versions 1.x, still evaluates code has additional double codes around it: ```less .rule { @var: "`(function(){console.log('Hello from JavaScript'); process.exit(1);})()`"; color: @var; } ``` ### Patches We decided to remove the inline JavaScript evaluation feature completely from the code of our Less.js fork. This fix is available in less-openui5 version [v0.10.0](https://github.com/SAP/less-openui5/releases/tag/v0.10.0) ### Workarounds Only process trusted theming resources. ### For more information If you have any questions or comments about this advisory: * Open an issue in https://github.com/SAP/less-openui5 * Email us at [email protected]