This script is used to perform a fast check if your server is possibly affected by CVE-2021-44228 (the log4j vulnerability). It does not give a 100% proof, that you are not vulnerable, but it gives a hint if it is possible, that you could be vulnerable.

• scans files for occurrences of log4j
• checks for packages containing log4j and Solr ElasticSearch
• checks if Java is installed
• Analyzes JAR/WAR/EAR files
• Option of checking hashes of .class files in archives

wget https://raw.githubusercontent.com/rubo77/log4j_checker_beta/main/log4j_checker_beta.sh -q -O - |bash

If you only want to see the warnings use

wget https://raw.githubusercontent.com/rubo77/log4j_checker_beta/main/log4j_checker_beta.sh -q -O - | bash | grep '\[WARNING\]'

The script can test .class files on the first level of JAR/WAR/EAR archives to see if they match with known sha256 hashes of vulnerable class files from log4j.
You have to provide a download of plain text file with sha256 hashes in HEX format, one per line, everything after first is ignored. The URL can be placed in variable download_file. Otherwise this feature will not operate.

The information Lunasec.io has put out about hashes of vulnerable binary Java .class files:

https://github.com/lunasec-io/lunasec/blob/master/tools/log4shell/constants/vulnerablehashes.go

We did not include an actual URL, set SHA256_HASHES_URL in the script or as first parameter on the shell.

Also see their blog: https://www.lunasec.io/docs/blog/log4j-zero-day-mitigation-guide/

The command locate has to to be installed, be sure to have locate up-to-date with:

sudo updatedb

The command unzip also needs to be installed, to inspect the jar files and hexdump is required. To install on Debian and Ubuntu systems:

sudo apt install unzip bsdmainutils

https://serverfault.com/questions/1086065/how-do-i-check-if-log4j-is-installed-on-my-server/1086132#1086132