CVE-2025-27818 is a high-severity vulnerability in Apache Kafka, specifically affecting Kafka Connect components from version 2.3.0 onward. The vulnerability arises from unsafe deserialization of untrusted data (CWE-502) via LDAP responses when an authenticated operator configures Kafka Connect connectors with malicious SASL JAAS configurations. An attacker with privileges to alter cluster configurations or create/modify connectors can set the `sasl.jaas.config` property to use the "com.sun.security.auth.module.LdapLoginModule". This causes the Kafka Connect server to connect to an attacker-controlled LDAP server, which can return crafted LDAP responses that trigger Java deserialization gadget chains. If vulnerable gadget classes are present in the classpath, this leads to remote code execution (RCE) on the Kafka Connect server. The vulnerability requires at least limited privileges (ability to alter cluster configs or connectors) and no user interaction. Since Apache Kafka 3.0.0, these properties can be set more easily in connector configurations, increasing the attack surface. Mitigations introduced in Kafka 3.9.1/4.0.0 include disabling dangerous login modules by default via the system property "-Dorg.apache.kafka.disallowed.login.modules" and allowing administrators to enforce connector client config override policies to restrict which Kafka client properties can be overridden. Users are advised to validate connector configurations to allow only trusted LDAP settings, audit connector dependencies for vulnerable versions, upgrade or remove risky connectors, and leverage the new system property and override policies to prevent exploitation. The CVSS 3.1 score is 8.8 (high), reflecting network attack vector, low attack complexity, required privileges, no user interaction, and high impact on confidentiality, integrity, and availability.

For European organizations using Apache Kafka, especially those deploying Kafka Connect clusters, this vulnerability poses a significant risk. Successful exploitation can lead to full remote code execution on Kafka Connect servers, potentially compromising sensitive data streams, disrupting critical data pipelines, and enabling lateral movement within enterprise networks. Given Kafka's widespread use in financial services, telecommunications, manufacturing, and public sector infrastructures across Europe, an attacker could leverage this vulnerability to exfiltrate confidential information, manipulate data integrity, or cause denial of service. The requirement for authenticated access to alter configurations limits exposure to insiders or attackers who have already breached perimeter defenses, but the impact remains severe. Organizations relying on Kafka Connect for integrating external data sources or sinks are particularly at risk if connector configurations are not tightly controlled. The vulnerability also raises compliance concerns under GDPR and other data protection regulations due to potential unauthorized data access and processing disruptions.

European organizations should implement the following specific mitigations: 1) Immediately audit all Kafka Connect cluster configurations and connector settings to identify any use of `sasl.jaas.config` properties referencing LDAP login modules, and remove or restrict them to trusted LDAP servers only. 2) Upgrade Apache Kafka to version 3.9.1 or later, where the system property `-Dorg.apache.kafka.disallowed.login.modules` disables dangerous login modules by default. 3) Define and enforce strict connector client config override policies to prevent unauthorized override of SASL JAAS configurations in connector definitions. 4) Review and update connector dependencies to eliminate vulnerable deserialization gadget classes from the classpath, or remove untrusted connectors altogether. 5) Implement strong access controls and monitoring on Kafka cluster administrative interfaces to prevent unauthorized configuration changes. 6) Employ network segmentation and firewall rules to restrict Kafka Connect servers’ outbound LDAP connections to only trusted servers. 7) Conduct regular security training for operators managing Kafka clusters to recognize and avoid risky configuration practices. 8) Monitor Kafka Connect logs and network traffic for suspicious LDAP connections or configuration changes indicative of exploitation attempts.