rgl/log4j-log4shell-playgroundA playground for poking at the Log4Shell (CVE-2021-44228) vulnerability mitigations
A playground for poking at the critical log4j (aka Log4Shell) (CVE-2021-44228) vulnerability mitigations.
This particular problem lies within the JndiLookup feature and the log4j ability to interpret ALL the arguments of a logging call.
I would expect it to only interpret the format message (the first argument of a logging call), e.g., the Hello {} in log.info("Hello {}", "${jndi:ldap://127.0.0.1:8081}"), but it interprests all of them.
The mitigations will prevent log4j from triggering the jndi lookups, but they still allow other lookups like ${java:version}.
NB: Since log4j 2.16.0 (LOG4J2-3211; diff) the format message is no longer interpreted.
This vulnerability can be triggered remotely when the target application logs any user supplied data, for example, from these common HTTP headers:
AcceptCookieLocationOriginRefererUser-AgentX-Api-VersionX-Forwarded-ForX-Forwarded-HostX-Requested-WithBuild:
sudo apt-get install -y openjdk-11-jdk-headless
wget https://archive.apache.org/dist/logging/log4j/2.10.0/apache-log4j-2.10.0-bin.tar.gz
wget https://archive.apache.org/dist/logging/log4j/2.16.0/apache-log4j-2.16.0-bin.tar.gz
tar xf apache-log4j-2.10.0-bin.tar.gz
tar xf apache-log4j-2.16.0-bin.tar.gz
javac -Werror -cp apache-log4j-2.10.0-bin/log4j-api-2.10.0.jar Server.java
Try a vulnerable log4j version:
java \
-cp apache-log4j-2.10.0-bin/log4j-api-2.10.0.jar:apache-log4j-2.10.0-bin/log4j-core-2.10.0.jar:. \
Server
curl -H 'X-Api-Version:${jndi:ldap://127.0.0.1:8081}' http://localhost:8080
curl -H 'X-Api-Version:${java:version}' http://localhost:8080
Try removing the JndiLookup class from the classpath mitigation:
cp apache-log4j-2.10.0-bin/log4j-core-2.10.0.jar log4j-core-2.10.0-without-jndi-lookup.jar
zip -q -d log4j-core-2.10.0-without-jndi-lookup.jar org/apache/logging/log4j/core/lookup/JndiLookup.class
java \
-cp apache-log4j-2.10.0-bin/log4j-api-2.10.0.jar:log4j-core-2.10.0-without-jndi-lookup.jar:. \
Server
curl -H 'X-Api-Version:${jndi:ldap://127.0.0.1:8081}' http://localhost:8080
curl -H 'X-Api-Version:${java:version}' http://localhost:8080
Try the environment variable mitigation:
NB Since 2021-12-15 (circa log4j 2.16.0 / CVE-2021-45046 release date) this is no longer recommended.
LOG4J_FORMAT_MSG_NO_LOOKUPS=true \
java \
-cp apache-log4j-2.10.0-bin/log4j-api-2.10.0.jar:apache-log4j-2.10.0-bin/log4j-core-2.10.0.jar:. \
Server
curl -H 'X-Api-Version:${jndi:ldap://127.0.0.1:8081}' http://localhost:8080
curl -H 'X-Api-Version:${java:version}' http://localhost:8080
Try a non-vulnerable log4j version:
java \
-cp apache-log4j-2.16.0-bin/log4j-api-2.16.0.jar:apache-log4j-2.16.0-bin/log4j-core-2.16.0.jar:. \
Server
curl -H 'X-Api-Version:${jndi:ldap://127.0.0.1:8081}' http://localhost:8080
curl -H 'X-Api-Version:${java:version}' http://localhost:8080
Try grype to see whether it detects the vulnerability:
wget https://github.com/anchore/grype/releases/download/v0.27.2/grype_0.27.2_linux_amd64.tar.gz
tar xf grype_0.27.2_linux_amd64.tar.gz grype
./grype dir:.
Try trivy to see whether it detects the vulnerability:
wget https://github.com/aquasecurity/trivy/releases/download/v0.21.2/trivy_0.21.2_Linux-64bit.tar.gz
tar xf trivy_0.21.2_Linux-64bit.tar.gz trivy
./trivy fs --security-checks vuln .