CVE-2021-21316

Processing untrusted theming resources might execute arbitrary code (ACE)

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]

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 of the Less.js library, it is an unexpected behavior in the context of OpenUI5 and SAPUI5 development.

Especially in the context of UI5 Tooling, which relies on less-openui5, this poses a security threat:

An attacker might create a library or 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:

.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 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:

.rule {
	@var: "`(function(){console.log('Hello from JavaScript'); process.exit(1);})()`";
	color: @var;
}

CVE-2021-21316 has a CVSS score of 6.3 (High). The vector is requires local access, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.10.0); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

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

1. What is CVE-2021-21316? CVE-2021-21316 is a high-severity security vulnerability in less-openui5 (npm), affecting versions < 0.10.0. It is fixed in 0.10.0.
2. How severe is CVE-2021-21316? CVE-2021-21316 has a CVSS score of 6.3 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of less-openui5 are affected by CVE-2021-21316? less-openui5 (npm) versions < 0.10.0 is affected.
4. Is there a fix for CVE-2021-21316? Yes. CVE-2021-21316 is fixed in 0.10.0. Upgrade to this version or later.
5. Is CVE-2021-21316 exploitable, and should I be worried? Whether CVE-2021-21316 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2021-21316 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2021-21316? Upgrade less-openui5 to 0.10.0 or later.