CVE-2021-45046: Apache Log4j2 Deserialization of Untrusted Data Vulnerability

Vulnerability summary

CVE-2021-45046 is a critical (CVSS 9.0) Expression Language Injection vulnerability in Apache Log4j2. It is known to be exploited: CISA lists it, first on 01-05-2023. It has been used in ransomware campaigns. EPSS estimates a 99.98% chance of exploitation in the next 30 days, higher than 99.9% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 14-12-2021
   PublishedVulnerability first disclosed.
2. 01-05-2023
   Added to CISA KEVApache Log4j2 Deserialization of Untrusted Data Vulnerability
3. 22-05-2023
   CISA remediation dueApply updates per vendor instructions.
4. 21-10-2025
   Last modifiedVulnerability information updated.

Description

It was found that the fix to address CVE-2021-44228 in Apache Log4j 2.15.0 was incomplete in certain non-default configurations. This could allows attackers with control over Thread Context Map (MDC) input data when the logging configuration uses a non-default Pattern Layout with either a Context Lookup (for example, $${ctx:loginId}) or a Thread Context Map pattern (%X, %mdc, or %MDC) to craft malicious input data using a JNDI Lookup pattern resulting in an information leak and remote code execution in some environments and local code execution in all environments. Log4j 2.16.0 (Java 8) and 2.12.2 (Java 7) fix this issue by removing support for message lookup patterns and disabling JNDI functionality by default.

• CWE-917Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')The product constructs all or part of an expression language (EL) statement in a framework such as a Java Server Page (JSP) using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended EL statement before it is executed.