CVE-2021-45046

CVE-2021-45046 is a critical-severity vulnerability in Apache Log4j with a CVSS 3.x base score of 9.0. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2023-05-01). The underlying weakness is classified as CWE-917.

Key facts

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.

Frequently asked questions

What is CVE-2021-45046?
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 has a CVSS 3.x base score of 9.0, rated critical severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-45046 being actively exploited?
Yes. CVE-2021-45046 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2023-05-01, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2021-45046?
CVE-2021-45046 primarily affects Apache Log4j. In total, 89 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-45046?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2021-45046 have an EU (EUVD) identifier?
Yes. CVE-2021-45046 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-34769. It is also flagged as exploited in the EUVD (since 2023-05-01).
When was CVE-2021-45046 published?
CVE-2021-45046 was published on 2021-12-14 and last updated on 2026-06-17.

References

Affected products (89)

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