CVE-2021-45046: Apache Log4j2 Deserialization of Untrusted Data Vulnerability
Status: confirmed exploited in the wild
CVE-2021-45046 appears in CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2023-05-01. Inclusion in KEV is not a severity prediction. It means CISA has reliable evidence that the vulnerability has actually been exploited against real targets, which is a stronger signal than a CVSS score on its own.
| Field | Value |
|---|---|
| CVE | CVE-2021-45046 |
| Vendor | Apache |
| Product | Log4j2 |
| Added to KEV | 2023-05-01 |
| Federal due date | 2023-05-22 |
| Ransomware campaign use | Known |
What the vulnerability 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.
Weakness classification
CISA classifies this entry under:
Required action
CISA's stated required action for this entry:
Apply updates per vendor instructions.
Ransomware context
CISA records this vulnerability as known to have been used in ransomware campaigns. That materially raises its priority relative to its CVSS score alone.
Federal remediation deadline
Under CISA Binding Operational Directive 22-01, U.S. federal civilian executive branch agencies were required to remediate this vulnerability by 2023-05-22. The directive does not bind private organisations, but the due date is a useful external signal: CISA sets shorter windows for what it assesses as higher risk.
Why KEV membership changes prioritisation
Most vulnerability backlogs are too large to clear, so the practical question is ordering rather than coverage. KEV is useful for that because it is evidence-based: an entry is on the list because exploitation was observed, not because a scoring formula predicted it might be.
A defensible triage rule used widely is to treat KEV membership as a promotion signal that overrides CVSS ranking, on the basis that a confirmed-exploited medium-severity issue generally warrants attention ahead of a theoretical critical one.
Determining whether you are affected
- Establish whether Apache Log4j2 is present anywhere in your estate, including indirectly and in systems not under active management.
- Identify the deployed versions and compare against the vendor advisory linked below.
- Apply the required action above, then confirm the change took effect rather than assuming it did.
Step one is where this usually fails. Several of the most costly incidents on record, including Code Red and Log4Shell, turned on organisations being unable to answer whether affected software was present at all.
How Safeguard helps
Safeguard's vulnerability management enriches findings with KEV and EPSS data, so an entry like this one surfaces as confirmed-exploited rather than sitting undifferentiated in a ranked list.
Sources
- CISA KEV catalog (version 2026.09.16): https://www.cisa.gov/known-exploited-vulnerabilities-catalog
- NVD record for CVE-2021-45046: https://nvd.nist.gov/vuln/detail/CVE-2021-45046
- Vendor and advisory references: https://logging.apache.org/log4j/2.x/security.html , https://nvd.nist.gov/vuln/detail/CVE-2021-45046
Catalog data retrieved from CISA KEV version 2026.09.16. Verify against the live catalog before relying on dates for compliance purposes.
