Goal

Detect successful exploits of the Log4shell vulnerability (CVE-2021-44228).

The vulnerability has CVSS Score: 10.0 CRITICAL and can lead to Remote Code Execution (RCE).

Strategy

Monitor payloads matching known patterns for CVE-2021-44228 (event rule: #sqr-000-017 ) and lookup for HTTP requests to load a Java class.

Generate an Application Security signal with CRITICAL severity.

Response

Consider blocking the attacking IP(s) temporarily to prevent them to reach deeper parts of your production systems.

Remediation

Considering the targeted application uses a vulnerable version of log4j and the default settings are disabled:

• Update log4j to the latest patched version immediately (>= 2.15.0)
• Disable lookups by setting formatMsgNoLookups=true. Only available from log4j >= 2.10 versions
• Use a non-vulnerable or empty implementation of the class org.apache.logging.log4j.core.lookup.JndiLookup
• Investigate the logs and the external class that is being called in the attack to check if the attacker successfully executed arbitrary code or not.