Apache Log4j StrSubstitutor Uncontrolled Recursion Denial-of-Service Vulnerability

December 19th, 2021
ZDI-21-1541 ZDI-CAN-16160

CVE ID

CVE-2021-45105

CVSS Score

5.3 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected Vendors

Apache

Affected Products

Log4j

Vulnerability Details

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.

Additional Details

Apache has issued an update to correct this vulnerability. More details can be found at:
https://logging.apache.org/log4j/2.x/security.html

Disclosure Timeline

  • 2021-12-15 - Vulnerability reported to vendor
  • 2021-12-19 - Coordinated public release of advisory

Credit

Guy Lederfein of Trend Micro Security Research

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