CVE-2021-45046
Apache Log4j2 Thread Context Message Pattern and Context Lookup Pattern vulnerable to a denial of service attack
- Published
- Dec 14, 2021
- Updated
- Oct 21, 2025
- Assigning CNA
- apache
- Evidence observed
- May 1, 2023
Primary CVSS
nvd · CVSS 3.1
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:HHigh · next 30 days
- Percentile
- 100.0%
- Model date
- Oct 17, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
CISA Known Exploited
This CVE appears in the CISA Known Exploited Vulnerabilities catalog.
Summary
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.
Sources
- Log4Shell HTTP ScannerModule
modules/auxiliary/scanner/http/log4shell_scanner.rb
Metasploit Framework modulesDeclared conditions
- verification: check_not_declared($.auxiliary_scanner/http/log4shell_scanner.check)
http/cves/2021/CVE-2021-45046.yaml
Nuclei TemplatesDeclared conditions
- network: http($.protocol_keys)
- verification: regex,word($.matchers[*].type)
- oob: interactsh_reference($.template_text)
Responsible use
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