Apache Log4j StrSubstitutor Uncontrolled Recursion Denial-of-Service Vulnerability [CVE-2021-45105]

Please note that this vulnerability is not the main well known Log4j one, for further information on CVE-2021-44228 please click here.

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.

Apache has issued an update to correct this vulnerability.

DISCLOSURE TIMELINE2021-12-15 – Vulnerability reported to vendor
2021-12-19 – Coordinated public release of advisory
CREDITGuy Lederfein of Trend Micro Security Research

More details can be found at:


Duncan is a technology professional with over 20 years experience of working in various IT roles. He has a interest in cyber security, and has a wide range of other skills in radio, electronics and telecommunications.

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