CVE-2025-11226: 
Apache Log4j vulnerability analysis and mitigation

CVE-2025-11226 is an Arbitrary Code Execution (ACE) vulnerability discovered in QOS.CH logback-core affecting versions up to and including 1.5.18. The vulnerability was disclosed on September 30, 2025, and affects Java applications using the logback-core library (NVD).

The vulnerability exists in the conditional configuration file processing functionality of logback-core. It allows attackers to execute arbitrary code through two attack vectors: by compromising an existing logback configuration file or by injecting an environment variable before program execution. The vulnerability requires the presence of both the Janino library and Spring Framework in the user's classpath. The CVSS v4.0 score is 5.9 (Medium) with the vector string CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:P/VC:H/VI:L/VA:L/SC:H/SI:L/SA:L/AU:N/RE:M/U:Green (NVD).

The vulnerability allows attackers with existing privileges to execute arbitrary code on affected systems. This can lead to complete system compromise if successfully exploited. The attack requires either write access to a configuration file or the ability to inject malicious environment variables (NVD).

The vulnerability has been fixed in logback version 1.5.19. The fix involves disallowing the 'new' operator in the condition attribute of elements. Users are advised to upgrade to version 1.5.19 or later to mitigate this vulnerability (Logback News).

The Apache James project responded quickly to the vulnerability by upgrading their logback dependency to version 1.5.19 to address the security issue (Apache Mail).