This update is not a security update per se. However, it contains a check in case of a missing or incorrect application secret and can thus protect a potentially vulnerable installation. The attack would be conceivable for any Symfony application independent of Contao.
About Contao 4.13 LTS
The first stable version of Contao 4.13 has been released on February 17, 2022, replacing Contao 4.9 as the long term support version. As an LTS version, 4.13 will be provided with bug fixes until February 14, 2025 and security-related updates until February 14, 2026. Contao 5.3 will be the next LTS version of Contao and will be released in February 2024, ensuring a stress-free transition.