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Known exploited · Apache

CVE-2021-44228: Apache Log4j2 Remote Code Execution Vulnerability

What it is

Apache Log4j2 contains a vulnerability where JNDI features do not protect against attacker-controlled JNDI-related endpoints, allowing for remote code execution.

Added December 10, 2021Due December 24, 2021CISA KEV catalog 2026.10.01

Vendor
Apache
Product
Log4j2
Added to KEV
December 10, 2021
CISA due date
December 24, 2021
Ransomware use
Known

What CISA requires

For all affected software assets for which updates exist, the only acceptable remediation actions are: 1) Apply updates; OR 2) remove affected assets from agency networks. Temporary mitigations using one of the measures provided at https://www.cisa.gov/uscert/ed-22-02-apache-log4j-recommended-mitigation-measures are only acceptable until updates are available.

Forensic triage

No

What to do now

  1. Find every instance of Log4j2 you run, including the forgotten ones, and check its version against the vendor advisory.
  2. Apply the vendor's fix or mitigation, before December 24, 2021 if you are bound by CISA's deadline, sooner if it faces the internet.
  3. Assume it was tried against you already: look for signs of exploitation from the date it was added, not from the day you patched.
  4. Until every instance is patched, block the attack at the edge: a WAF in blocking mode stops Java deserialization payloads.

References

CVE-2021-44228 in the National Vulnerability Database

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Source: CISA Known Exploited Vulnerabilities Catalog (public domain), catalog version 2026.10.01.