What is the Spring4Shell exploit? An overview of the Spring vulnerability

Spring4Shell is a newly disclosed vulnerability affecting the Spring "spring-beans" library on Java 9+ with Tomcat 9+, which can allow an attacker to write a malicious payload to disk and execute it. The report outlines how to validate exposure (check Java/Tomcat versions, inspect WAR contents for spring-bean jars or CachedIntrospectionResults.class, and confirm use of Spring parameter binding to POJOs), notes proof-of-concept code and YARA detection rules are publicly available, states no confirmed exploitation in the wild at the time, and advises monitoring logs and validating Java applications; no official patch was available when published.