Known exploited · Apache

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

What it is

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.

Added May 1, 2023Due May 22, 2023CISA KEV catalog 2026.10.01

Vendor: Apache
Product: Log4j2
Added to KEV: May 1, 2023
CISA due date: May 22, 2023
Ransomware use: Known
Weakness: CWE-917: Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')

What CISA requires

Apply updates per vendor instructions.

Forensic triage

What to do now

Find every instance of Log4j2 you run, including the forgotten ones, and check its version against the vendor advisory.
Apply the vendor's fix or mitigation, before May 22, 2023 if you are bound by CISA's deadline, sooner if it faces the internet.
Assume it was tried against you already: look for signs of exploitation from the date it was added, not from the day you patched.
Until every instance is patched, block the attack at the edge: a WAF in blocking mode stops Log4Shell (JNDI lookup) payloads.

References

CVE-2021-45046 in the National Vulnerability Database

The Dome

Block it at the edge while you patch

The Dome's WAF runs the OWASP Core Rule Set in blocking mode and stops Log4Shell (JNDI lookup) payloads before they reach your application.

See the Dome

T Academy

Train the engineers who fix it

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