CVE-2021-45046
Apache Log4j2 Deserialization of Untrusted Data Vulnerability
Apache Log4j2
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, $${ctx:loginId}) or a Thread Context Map pattern (%X, %mdc, or %MDC) to craft malicious input data using a JNDI Lookup pattern resulting in an information leak and remote code execution in some environments and local code execution in all environments. Log4j 2.16.0 (Java 8) and 2.12.2 (Java 7) fix this issue by removing support for message lookup patterns and disabling JNDI functionality by default.
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 1 May 2023. US federal agencies were required to remediate it by 22 May 2023. CISA records this vulnerability as known to be used in ransomware campaigns.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 100%, which is higher than 99.9% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Frequently asked questions
Is CVE-2021-45046 being exploited by ransomware groups?
No ransomware group in this database is currently recorded as exploiting CVE-2021-45046.
What does CVE-2021-45046 affect?
CVE-2021-45046 affects Apache Log4j2. It was found that the fix to address CVE-2021-44228 in Apache Log4j 2.15.0 was incomplete in certain non-default configurations. This could allows attackers with control over Thread Context Map (MDC) input data when the logging configuration uses a non-default Pattern Layout with either a Context Lookup (for example, $${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.
How severe is CVE-2021-45046?
CVE-2021-45046 is rated CRITICAL with a CVSS base score of 9. EPSS puts the probability of exploitation in the next 30 days at 100%, higher than 99.9% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 22 May 2023.
How should organisations respond to CVE-2021-45046?
Apply the vendor patch for Apache Log4j2 as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.