CVE-2026-9558 is a critical-severity security vulnerability in mautic/core (composer), affecting versions >= 1.3.0, < 4.4.13. It is fixed in 5.2.11, 6.0.9, 7.1.2.
Summary A Server-Side Template Injection (SSTI) vulnerability exists in Mautic's theme engine. The platform renders uploaded Twig templates without a sandbox or strict function restrictions. Authenticated users with permissions to create or upload themes can abuse this to execute arbitrary code. Impact An authenticated user with theme upload and creation privileges can bypass boundaries to execute arbitrary system commands on the hosting server (Remote Code Execution) or access restricted system files and configuration settings. Patched Versions This security issue has been addressed in the following releases: 7.1.2 6.0.9 5.2.11 For users on Mautic 4.x, this fix is available in: 4.4.20 via ELTS Mautic strongly recommend upgrading to a patched version immediately. Workarounds There are no official workarounds. To mitigate this vulnerability without upgrading, restrict theme upload and creation permissions (core:themes:create) to only highly trusted administrators.
CVE-2026-9558 has a CVSS score of 9.9 (Critical). The vector is network-reachable, low 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 (5.2.11, 6.0.9, 7.1.2). Upgrading removes the vulnerable code path.
composer
mautic/core (>= 1.3.0, < 4.4.13)mautic/core (>= 5.0.0, < 5.2.11)mautic/core (>= 6.0.0, < 6.0.9)mautic/core (>= 7.0.0, < 7.1.2)mautic/core → 5.2.11 (composer)mautic/core → 6.0.9 (composer)mautic/core → 7.1.2 (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-2026-9558 is reachable in your applications. Explore open-source security for your team.
See if CVE-2026-9558 is reachable in your applications. Get a demo
Already deployed Kodem? See CVE-2026-9558 in your environment →Upgrade the following packages to resolve this vulnerability:
mautic/core to 5.2.11 or latermautic/core to 6.0.9 or latermautic/core to 7.1.2 or laterKodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2026-9558 is a critical-severity security vulnerability in mautic/core (composer), affecting versions >= 1.3.0, < 4.4.13. It is fixed in 5.2.11, 6.0.9, 7.1.2.
CVE-2026-9558 has a CVSS score of 9.9 (Critical). 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 >= 1.3.0, < 4.4.13 is affected.
Yes. CVE-2026-9558 is fixed in 5.2.11, 6.0.9, 7.1.2. Upgrade to this version or later.
Whether CVE-2026-9558 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 5.2.11 or latermautic/core to 6.0.9 or latermautic/core to 7.1.2 or later