Applications that are vulnerable to the log4j CVE-2021-44228 issue may be detectable by scanning jar, war, and ear files to search for the presence of JndiLookup.class.

Depending on the platform that you are investigating, the PowerShell or the Python3 script may make more sense to run. In both cases, the optional argument is the top-level directory that you would like to use to begin your search.

Any file discovered is worth investigation to determine if the application using it is vulnerable. For any JndiLookup.class that is present, log4j commonly includes the version in the jar file name. For example, a hit on log4j-core-2.14.1.jar would be indicative of a vulnerable application. Alternatively, log4j-core-2.16.jar may also produce a hit because the JndiLookup code is still present in the 2.16 version of log4j, but it is disabled by default. See VU#930724 for more details.

For example, here is an invocation of the PowerShell version of the scanner:

Similarly, here is an invocation of the Python3 version:

Finally, here is an invocation of the Bash version:

Note that the Bash and Python versions of this script will by design limit scans to a single filesystem. With the PowerShell version, locations to scan can be piped into the script to have control of what is checked. For example, to scan a list of paths conatined in a the file paths.txt:

get-content .\paths.txt | .\checkjndi.ps1

Let's look at the first hit on our Windows scan execution:

WARNING: C:\tmp\2.15\log4j-core-2.15.0.jar contains org/apache/logging/log4j/core/lookup/JndiLookup.class

Based on the jar name, this is a library from log4j 2.15. While this version of log4j fixes CVE-2021-44228, it still contained a flaw that is outlined as CVE-2021-45046. The impact of CVE-2021-45046 is a denial of service for only certain Java applications that use log4j 2.15. For Java applications that use log4j versions prior to 2.15 and that also fit the prerequisites for CVE-2021-45046 applying, the impact is RCE.

Let's look at the second hit:

C:\tmp\2.16\log4j-core-2.16.0.jar contains org/apache/logging/log4j/core/lookup/JndiLookup.class ** BUT APPEARS TO BE PATCHED **

This jar file contains a 2.16 version of log4j, which is not vulnerable to CVE-2021-44228. This result is reported for information purposes, which shows that a vendor has patched their product.

Let's look at the third hit:

WARNING: C:\tmp\ghidra_10.0_PUBLIC\Ghidra\Framework\Generic\lib\log4j-core-2.12.1.jar contains org/apache/logging/log4j/core/lookup/JndiLookup.class

Here we can see that Ghidra uses log4j version 2.12.1, and as such we should assume it to be vulnerable. And indeed, Ghidra versions before 10.1 are vulnerable to CVE-2021-44228.

You should investigate any hits reported by either of these scripts, and confirm that either the log4j version is indeed the fixed 2.16 version, or reach out to your software vendor to obtain a fixed version of the software. Alternatively, VU#930724 has information about how JndiLookup.class can be removed from vulnerable jar files.

The PowerShell version of the scanner has additional error reporting when files or directories cannot be investigated. In particular, any Unable to scan errors reporting UnauthorizedAccessException is indicative of a permission problem in accessing a directory and/or a file. Any Unable to scan errors reporting InvalidDataException is usually due to a corrupt archive.