CVEs / CVE-2021-45046

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

• Known exploited in the CISA KEV catalog since 1 May 2023
• critical 9 CVSS 3.1 (NVD)
• EPSS 99.9% chance of exploitation in the next 30 days, higher than 99% of CVEs (30 Oct 2026)
• Last changed at its sources 26 Oct 2026

Summary

Apache Log4j2 contains a deserialization of untrusted data vulnerability due to the incomplete fix of CVE-2021-44228, where the Thread Context Lookup Pattern is vulnerable to remote code execution in certain non-default configurations.

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.

Affected and fixed versions

Package versions from GHSA-7rjr-3q55-vv33.

Exploitation

Severity

References

• CVE-2021-45046 on NVD
• CVE-2021-45046 in the CISA KEV catalog
• https://logging.apache.org/log4j/2.x/security.html (cited by CISA)
• CVE-2021-45046 on OSV
• http://www.openwall.com/lists/oss-security/2021/12/14/4 Mailing List, Mitigation, Third Party Advisory
• http://www.openwall.com/lists/oss-security/2021/12/15/3 Mailing List, Third Party Advisory
• http://www.openwall.com/lists/oss-security/2021/12/18/1 Mailing List, Third Party Advisory
• https://cert-portal.siemens.com/productcert/pdf/ssa-397453.pdf Third Party Advisory
• https://cert-portal.siemens.com/productcert/pdf/ssa-479842.pdf Third Party Advisory
• https://cert-portal.siemens.com/productcert/pdf/ssa-661247.pdf Third Party Advisory
• https://cert-portal.siemens.com/productcert/pdf/ssa-714170.pdf Third Party Advisory
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EOKPQGV24RRBBI4TBZUDQMM4MEH7MXCY/ Mailing List, Release Notes
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SIG7FZULMNK2XF6FZRU4VWYDQXNMUGAJ/ Mailing List, Release Notes
• https://logging.apache.org/log4j/2.x/security.html Mitigation, Release Notes, Vendor Advisory
• https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0032 Third Party Advisory
• https://security.gentoo.org/glsa/202310-16 Third Party Advisory
• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-log4j-qRuKNEbd Third Party Advisory
• https://www.cve.org/CVERecord?id=CVE-2021-44228 Not Applicable
• https://www.debian.org/security/2021/dsa-5022 Third Party Advisory
• https://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-00646.html Third Party Advisory
• https://www.kb.cert.org/vuls/id/930724 Third Party Advisory, US Government Resource
• https://www.oracle.com/security-alerts/alert-cve-2021-44228.html Third Party Advisory
• https://www.oracle.com/security-alerts/cpuapr2022.html Third Party Advisory
• https://www.oracle.com/security-alerts/cpujan2022.html Patch, Third Party Advisory