CVE-2021-45105

Apache Log4j2 versiones 2.0-alpha1 hasta 2.16.0 (excluyendo las versiones 2.12.3 y 2.3.1) no protegían de la recursión no controlada de las búsquedas autorreferenciales. Esto permite a un atacante con control sobre los datos de Thread Context Map causar una denegación de servicio cuando es interpretada una cadena diseñada. Este problema se ha corregido en Log4j versiones 2.17.0, 2.12.3 y 2.3.1

A flaw was found in the Apache Log4j logging library 2.x. when the logging configuration uses a non-default Pattern Layout with a Context Lookup. Attackers with control over Thread Context Map (MDC) input data can craft malicious input data that contains a recursive lookup and can cause Denial of Service.

This vulnerability allows remote attackers to create a denial-of-service condition on affected installations of Apache Log4j. Authentication is not required to exploit this vulnerability.
The specific flaw exists within the StrSubstitutor class. The issue results from the lack of proper validation of user-supplied data, which can result in a resource exhaustion condition. An attacker can leverage this vulnerability to create a denial-of-service condition on the process.