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.
Impact Insufficient sanitization / filtering allows for arbitrary JavaScript Injection in Mautic using the bounce management callback function. The values submitted in the "error" and "errorrelatedto" 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 "errorrelatedto" 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. Patches Upgrade to 3.3.4 or 4.0.0 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]
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.
composer
mautic/core (< 3.3.4)mautic/core (>= 4.0.0-alpha1, < 4.0.0)mautic/core → 3.3.4 (composer)mautic/core → 4.0.0 (composer)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 instead of chasing every advisory.
Kodem's runtime-powered SCA identifies whether CVE-2021-27910 is reachable in your applications. Explore open-source security for your team.
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Already deployed Kodem? See CVE-2021-27910 in your environment →Upgrade the following packages to resolve this vulnerability:
mautic/core to 3.3.4 or latermautic/core to 4.0.0 or laterKodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
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.
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.
mautic/core (composer) versions < 3.3.4 is affected.
Yes. CVE-2021-27910 is fixed in 3.3.4, 4.0.0. Upgrade to this version or later.
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
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.
mautic/core to 3.3.4 or latermautic/core to 4.0.0 or later