CVE-2021-27910

Stored XSS vulnerability on Bounce Management Callback

Workarounds

No

References

https://github.com/mautic/mautic/releases/tag/3.3.4
https://github.com/mautic/mautic/releases/tag/4.0.0

For more information

If you have any questions or comments about this advisory:

• Email us at [email protected]

Insufficient sanitization / filtering allows for arbitrary JavaScript Injection in Mautic using the bounce management callback function. The values submitted in the "error" and "error_related_to" parameters of the POST request of the bounce management callback will be permanently stored and executed once the details page of an affected lead is opened by a Mautic user.

An attacker with access to the bounce management callback function (identified with the Mailjet webhook, but it is assumed this will work uniformly across all kinds of webhooks) can inject arbitrary JavaScript Code into the "error" and "error_related_to" parameters of the POST request (POST /mailer/<product / webhook>/callback). It is noted that there is no authentication needed to access this function.

The JavaScript Code is stored permanently in the web application and executed every time an authenticated user views the details page of a single contact / lead in Mautic. This means, arbitrary code can be executed to, e.g., steal or tamper with information.

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-2021-27910 has a CVSS score of 8.2 (High). The vector is network-reachable, 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 (3.3.4, 4.0.0); upgrading removes the vulnerable code path.

Kodem intelligence

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Upgrade to 3.3.4 or 4.0.0

1. What is CVE-2021-27910? CVE-2021-27910 is a high-severity cross-site scripting (XSS) vulnerability in mautic/core (composer), affecting versions < 3.3.4. It is fixed in 3.3.4, 4.0.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2021-27910? CVE-2021-27910 has a CVSS score of 8.2 (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 mautic/core are affected by CVE-2021-27910? mautic/core (composer) versions < 3.3.4 is affected.
4. Is there a fix for CVE-2021-27910? Yes. CVE-2021-27910 is fixed in 3.3.4, 4.0.0. Upgrade to this version or later.
5. Is CVE-2021-27910 exploitable, and should I be worried? Whether CVE-2021-27910 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-2021-27910 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-2021-27910?
   • Upgrade mautic/core to 3.3.4 or later
   • Upgrade mautic/core to 4.0.0 or later

Other vulnerabilities in mautic/core