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

- Exploited (CISA KEV): yes, added 2023-05-01, known ransomware use
- Published: 2021-12-14
- CVSS: 9 CRITICAL (v3.1)
- EPSS: 100.0% (100th percentile)
- CWE: CWE-917

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.

## Edge WAF coverage (claimed by vendors, not measured)

| Vendor | Status | First rule | Days after publication |
|---|---|---|---|
| Cloudflare | Before feed history | — | — |
| AWS | No public claim | — | — |
| Microsoft Azure | Rule published | — | — |
| Google Cloud | Rule published | — | — |
| Fastly | Before feed history | — | — |
| F5 | Before feed history | — | — |
| Akamai | No public source | — | — |
| OWASP CRS | Before feed history | — | — |

### Microsoft Azure

- undated · listed · rule 944240
  > Rule 944240: Critical - 5 · 2 · Remote Command Execution: Java serialization and Log4j vulnerability (CVE-2021-44228, CVE-2021-45046)
  Source: https://learn.microsoft.com/en-us/azure/web-application-firewall/afds/waf-front-door-drs
- undated · listed · rule 944240
  > Rule 944240: Critical - 5 · 2 · Remote Command Execution: Java serialization and Log4j vulnerability (CVE-2021-44228, CVE-2021-45046)
  Source: https://learn.microsoft.com/en-us/azure/web-application-firewall/ag/application-gateway-crs-rulegroups-rules
- undated · listed · rule 800100
  > Rule 800100: Critical - 5 · PL2 · Rule to help detect and mitigate log4j vulnerability CVE-2021-44228, CVE-2021-45046
  Source: https://learn.microsoft.com/en-us/azure/web-application-firewall/ag/application-gateway-crs-rulegroups-rules

### Google Cloud

- undated · listed · rule owasp-crs-v030001-id044228-cve
  > Signature owasp-crs-v030001-id044228-cve (sensitivity 1): Base rule to help detect exploit attempts of CVE-2021-44228 & CVE-2021-45046
  Source: https://docs.cloud.google.com/armor/docs/waf-rules

## Our test (measured)

- OWASP Core Rule Set 4.25.0, paranoia level 1, anomaly threshold 5, default CRS settings: blocked (1 of 1 requests blocked), template CVE-2021-45046, 2026-11-02
- OWASP Core Rule Set 4.25.0, paranoia level 2, anomaly threshold 5, default CRS settings: blocked (1 of 1 requests blocked), template CVE-2021-45046, 2026-11-02

"No public claim" means no vendor statement names this CVE; "Before feed history" means the CVE is older than the vendor feed. In both cases generic rules may still block it.

HTML: https://cve.vigilbase.com/cve/CVE-2021-45046 · JSON: https://cve.vigilbase.com/api/v1/cves/CVE-2021-45046