What is CVE-2021-21365?

CVE-2021-21365 is a medium-severity cross-site scripting (XSS) vulnerability in bk2k/bootstrap-package (composer), affecting versions >= 7.1.0, < 7.1.2. It is fixed in 7.1.2, 8.0.8, 9.0.4, 9.1.3, 10.0.10, 11.0.3. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.

How severe is CVE-2021-21365?

CVE-2021-21365 has a CVSS score of 5.4 (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.

Which versions of bk2k/bootstrap-package are affected by CVE-2021-21365?

bk2k/bootstrap-package (composer) versions >= 7.1.0, < 7.1.2 is affected.

Is there a fix for CVE-2021-21365?

Yes. CVE-2021-21365 is fixed in 7.1.2, 8.0.8, 9.0.4, 9.1.3, 10.0.10, 11.0.3. Upgrade to this version or later.

Is CVE-2021-21365 exploitable, and should I be worried?

Whether CVE-2021-21365 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.

What actually determines whether CVE-2021-21365 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.

How do I fix CVE-2021-21365?

Upgrade: bk2k/bootstrap-package to 7.1.2 or later, bk2k/bootstrap-package to 8.0.8 or later, bk2k/bootstrap-package to 9.0.4 or later, bk2k/bootstrap-package to 9.1.3 or later, bk2k/bootstrap-package to 10.0.10 or later, bk2k/bootstrap-package to 11.0.3 or later.

CVE-2021-21365 in bk2k/bootstrap-package

Q: How severe is CVE-2021-21365?

CVE-2021-21365 has a CVSS score of 5.4 (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.

Q: Which versions of bk2k/bootstrap-package are affected by CVE-2021-21365?

bk2k/bootstrap-package (composer) versions >= 7.1.0, < 7.1.2 is affected.

Q: Is there a fix for CVE-2021-21365?

Yes. CVE-2021-21365 is fixed in 7.1.2, 8.0.8, 9.0.4, 9.1.3, 10.0.10, 11.0.3. Upgrade to this version or later.

Q: Is CVE-2021-21365 exploitable, and should I be worried?

Whether CVE-2021-21365 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.

Q: What actually determines whether CVE-2021-21365 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.

Q: How do I fix CVE-2021-21365?

Upgrade: bk2k/bootstrap-package to 7.1.2 or later, bk2k/bootstrap-package to 8.0.8 or later, bk2k/bootstrap-package to 9.0.4 or later, bk2k/bootstrap-package to 9.1.3 or later, bk2k/bootstrap-package to 10.0.10 or later, bk2k/bootstrap-package to 11.0.3 or later.

Summary

Cross-Site Scripting in Bootstrap Package

Problem

It has been discovered that rendering content in the website frontend is vulnerable to cross-site scripting. A valid backend user account is needed to exploit this vulnerability.

The following templates are affected by the vulnerability:

Resources/Private/Partials/ContentElements/Carousel/Item/CallToAction.html
Resources/Private/Partials/ContentElements/Carousel/Item/Header.html
Resources/Private/Partials/ContentElements/Carousel/Item/Text.html
Resources/Private/Partials/ContentElements/Carousel/Item/TextAndImage.html
Resources/Private/Partials/ContentElements/Header/SubHeader.html

Users of the extension, who have overwritten the affected templates with custom code must manually apply the security fix as shown in this Git commit.

Credits

Thanks to TYPO3 security team member Oliver Hader who reported and fixed the issue.

Impact

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2021-21365 has a CVSS score of 5.4 (Medium). The vector is network-reachable, low 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 (7.1.2, 8.0.8, 9.0.4, 9.1.3, 10.0.10, 11.0.3); upgrading removes the vulnerable code path.

Affected versions

bk2k/bootstrap-package (>= 7.1.0, < 7.1.2) bk2k/bootstrap-package (>= 8.0.0, < 8.0.8) bk2k/bootstrap-package (>= 9.0.0, < 9.0.4) bk2k/bootstrap-package (>= 9.1.0, < 9.1.3) bk2k/bootstrap-package (>= 10.0.0, < 10.0.10) bk2k/bootstrap-package (>= 11.0.0, < 11.0.3)

Security releases

bk2k/bootstrap-package → 7.1.2 (composer) bk2k/bootstrap-package → 8.0.8 (composer) bk2k/bootstrap-package → 9.0.4 (composer) bk2k/bootstrap-package → 9.1.3 (composer) bk2k/bootstrap-package → 10.0.10 (composer) bk2k/bootstrap-package → 11.0.3 (composer)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

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Remediation advice

Update to version 7.1.2, 8.0.8, 9.0.4, 9.1.3, 10.0.10 or 11.0.3 of the Bootstrap Package that fix the problem described.

Updated version are available from the TYPO3 extension manager, Packagist and at https://extensions.typo3.org/extension/download/bootstrap_package/.

Frequently Asked Questions

What is CVE-2021-21365? CVE-2021-21365 is a medium-severity cross-site scripting (XSS) vulnerability in bk2k/bootstrap-package (composer), affecting versions >= 7.1.0, < 7.1.2. It is fixed in 7.1.2, 8.0.8, 9.0.4, 9.1.3, 10.0.10, 11.0.3. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
How severe is CVE-2021-21365? CVE-2021-21365 has a CVSS score of 5.4 (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.
Which versions of bk2k/bootstrap-package are affected by CVE-2021-21365? bk2k/bootstrap-package (composer) versions >= 7.1.0, < 7.1.2 is affected.
Is there a fix for CVE-2021-21365? Yes. CVE-2021-21365 is fixed in 7.1.2, 8.0.8, 9.0.4, 9.1.3, 10.0.10, 11.0.3. Upgrade to this version or later.
Is CVE-2021-21365 exploitable, and should I be worried? Whether CVE-2021-21365 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
What actually determines whether CVE-2021-21365 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.
How do I fix CVE-2021-21365?
- Upgrade bk2k/bootstrap-package to 7.1.2 or later
- Upgrade bk2k/bootstrap-package to 8.0.8 or later
- Upgrade bk2k/bootstrap-package to 9.0.4 or later
- Upgrade bk2k/bootstrap-package to 9.1.3 or later
- Upgrade bk2k/bootstrap-package to 10.0.10 or later
- Upgrade bk2k/bootstrap-package to 11.0.3 or later