CVE-2021-21353

Remote code execution via the pretty option.

Workarounds

If there is no way for un-trusted input to be passed to pug as the pretty option, e.g. if you compile templates in advance before applying user input to them, you do not need to upgrade.

References

Original report: https://github.com/pugjs/pug/issues/3312

For more information

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If a remote attacker was able to control the pretty option of the pug compiler, e.g. if you spread a user provided object such as the query parameters of a request into the pug template inputs, it was possible for them to achieve remote code execution on the node.js backend.

Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.

CVE-2021-21353 has a CVSS score of 6.8 (Medium). The vector is network-reachable, no privileges required, and no user interaction. 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 (3.0.1, 2.0.3, 3.0.2); upgrading removes the vulnerable code path.

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1. What is CVE-2021-21353? CVE-2021-21353 is a medium-severity code injection vulnerability in pug (npm), affecting versions < 3.0.1. It is fixed in 3.0.1, 2.0.3, 3.0.2. Untrusted input is evaluated as executable code within the application's runtime environment.
2. How severe is CVE-2021-21353? CVE-2021-21353 has a CVSS score of 6.8 (Medium). 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 packages are affected by CVE-2021-21353?
   • pug (npm) (versions < 3.0.1)
   • pug-code-gen (npm) (versions < 2.0.3)
4. Is there a fix for CVE-2021-21353? Yes. CVE-2021-21353 is fixed in 3.0.1, 2.0.3, 3.0.2. Upgrade to this version or later.
5. Is CVE-2021-21353 exploitable, and should I be worried? Whether CVE-2021-21353 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-2021-21353 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-2021-21353?
   • Upgrade pug to 3.0.1 or later
   • Upgrade pug-code-gen to 2.0.3 or later
   • Upgrade pug-code-gen to 3.0.2 or later

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