CVE-2021-4104
Log4j 1.2 JMSAppender RCE: stopped at runtime
Waratek RASP already blocks this exploit at runtime, inside the JVM - with no application change, no vendor patch, and no downtime.
Published December 14, 2021 · Updated June 30, 2026
The vulnerability
Remote code execution via JNDI lookup
When Log4j 1.2 is specifically configured to use JMSAppender, an attacker with write access to the logging configuration can set TopicBindingName and TopicConnectionFactoryBindingName to point at an attacker-controlled JNDI resource, resulting in remote code execution similar to Log4Shell.
Running an affected version? We can help.
Waratek RASP shields the vulnerable code in production - the exploit is blocked at runtime with no library upgrade, no redeploy, and no downtime. We can have you covered fast.
How Waratek RASP stops it
Blocked at runtime by Waratek RASP
Waratek RASP ships a patch rule that blocks exploitation at the exact point the dangerous operation is attempted, inside the JVM.
Runtime, not perimeter
Waratek RASP acts inside the JVM at the exact call that turns input into code, so obfuscated and encoded payloads are caught where a WAF misses them.
No code changes
Protection is applied as a rule at runtime. No source edits, no recompilation, no library upgrade, and no application restart required.
Zero false positives
Rules target the specific unsafe behaviour of the exploit, so legitimate traffic keeps flowing while the attack is blocked and logged.
| Mod | Rules | Enable |
|---|---|---|
| Log4j 1.2 JMSAppender RCE protectionCVE-2021-4104 · Deserialization of untrusted data | 1 | |
| SQL Injection protectionQuery manipulation | 4 | |
| Path Traversal protectionUnsafe file access | 3 |
Flip one toggle in the Waratek Portal. The protection deploys to every attached application, with no restart.
Common questions
Log4j 1.2 JMSAppender RCE FAQ
Is Log4j 1.2 JMSAppender RCE (CVE-2021-4104) exploitable?
CVE-2021-4104 carries a CVSS 7.5/10 (HIGH) rating and affects Apache Log4j 1.2 (JMSAppender) Log4j 1.2 (end-of-life since 2015), when configured to use JMSAppender. When Log4j 1.2 is specifically configured to use JMSAppender, an attacker with write access to the logging configuration can set TopicBindingName and TopicConnectionFactoryBindingName to point at an attacker-controlled JNDI resource, resulting in remote code execution similar to Log4Shell.
How does Waratek mitigate Log4j 1.2 JMSAppender RCE (CVE-2021-4104)?
Waratek RASP blocks exploitation of Log4j 1.2 JMSAppender RCE (CVE-2021-4104) inside the JVM at runtime, with no application code changes, no vendor patch and no restart.
How quickly was Log4j 1.2 JMSAppender RCE (CVE-2021-4104) exploited after disclosure?
A working exploit for CVE-2021-4104 was published within hours of its NVD disclosure, on December 14, 2021.
Protect your apps in production
Get protected against Log4j 1.2 JMSAppender RCE - without code changes or redeploying
Book a call and we’ll show you how Waratek RASP shields your running applications against CVE-2021-4104 and attacks like it, and get you covered in production.