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https://github.com/nccgroup/log4j-jndi-be-gone
A Byte Buddy Java agent-based fix for CVE-2021-44228, the log4j 2.x "JNDI LDAP" vulnerability.
https://github.com/nccgroup/log4j-jndi-be-gone
Last synced: 3 months ago
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A Byte Buddy Java agent-based fix for CVE-2021-44228, the log4j 2.x "JNDI LDAP" vulnerability.
- Host: GitHub
- URL: https://github.com/nccgroup/log4j-jndi-be-gone
- Owner: nccgroup
- License: apache-2.0
- Created: 2021-12-12T15:29:20.000Z (almost 3 years ago)
- Default Branch: main
- Last Pushed: 2022-01-04T02:03:58.000Z (almost 3 years ago)
- Last Synced: 2024-05-13T19:33:47.432Z (6 months ago)
- Language: Java
- Homepage: https://research.nccgroup.com/2021/12/12/log4j-jndi-be-gone-a-simple-mitigation-for-cve-2021-44228/
- Size: 80.1 KB
- Stars: 71
- Watchers: 12
- Forks: 17
- Open Issues: 3
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
- awesome-hacking-lists - nccgroup/log4j-jndi-be-gone - A Byte Buddy Java agent-based fix for CVE-2021-44228, the log4j 2.x "JNDI LDAP" vulnerability. (Java)
README
# log4j-jndi-be-gone
A [Byte Buddy](https://bytebuddy.net/) Java agent-based fix for CVE-2021-44228,
the log4j 2.x "JNDI LDAP" vulnerability.
It does three things:
* Disables the internal method handler for `jndi:` format strings ("lookups").
* Logs a message to `System.err` (i.e stderr) indicating that a log4j JNDI
attempt has been made (including the format string attempted, with any `${}`
characters sanitized to prevent transitive injections).
* Resolves the format string to `"(log4j jndi disabled)"` in the log message
(to prevent transitive injections).
# Usage
Add `-javaagent:path/to/log4j-jndi-be-gone-1.0.0-standalone.jar` to your `java` commands.
***Note:*** If you already have Byte Buddy in the classpath, try using
`log4j-jndi-be-gone-1.0.0.jar`.
```
$ java -javaagent:path/to/log4j-jndi-be-gone-1.0.0-standalone.jar -jar path/to/some.jar
```
As of version 1.1.0, log4j-jndi-be-gone defaults to attempting to handle
repackaged (aka "shaded") versions of log4j that may be embedded in a JAR under
an alternate package name to prevent collisions between an application's
version of a depdencency and a depdendency's version of the same depdendency.
However, it should be noted that log4j seems not to easily be repckaged under
alternate package names/prefixes due to the use of reflection with static
classnames and/or classnames from embedded configuration files.
This behavior can be disabled by placing `=structureMatch=0` after the agent JAR path
in the `-javaagent:` argument, e.g.:
```
-javaagent:path/to/log4j-jndi-be-gone-1.0.0-standalone.jar=structureMatch=0
```
which will result in the same matching behavior as 1.0.0, a simple exact string
comparison against the class name.
# Obtaining log4j-jndi-be-gone
You can build the JAR with `./gradlew` (`build/libs/log4j-jndi-be-gone-1.0.0(-standalone).jar`)
or get it from the [releases page](https://github.com/nccgroup/log4j-jndi-be-gone/releases).
# Compatibility
The log4j-jndi-be-gone agent JAR supports Java 6-17+.
## Class Matching
The implementation starts by matching against classes with suffixes that match
the innermost sub-packages and classname of
`org.apache.logging.log4j.core.lookup.JndiLookup`,
`lookup.JndiLookup`, as `org.apache.logging.log4j.core` can reasonably be
expected to have been mangled by repackaging rules that did not seek to
preserve package names. Additionally, instead of just performing similar checks
for all other expected log4j types, it ensures that they exist under the same
base package as well.
The implementation then walks through the structure of any identified potential
log4j `lookup.JndiLookup` classes, attempting to validate against:
* the modifiers on the class itself
* the class' parent class and/or implemented interfaces (these differ between
log4j versions)
* the `org.apache.logging.log4j.core.config.plugins.Plugin` annotation expected
across all 2.x versions, including annotation parameters and their values
* the method `lookup()`, matching against its modifiers and type signature
(and ignoring the 1-argument version from 2.0)
* the method `convertJndiName()`, matching against its modifiers and type signature
* the field `CONTAINER_JNDI_RESOURCE_PATH_PREFIX`, matching against its modifiers
# Caveats
* log4j-jndi-be-gone will not work if the log4j library has been obfuscated or
if its class packages/names have been modified other than basic re-packaging
(i.e. "shading").
* FWIW, log4j 2.x is pretty inflexible with regards to being repackaged, so
it's unclear how common such practices are.
* `log4j-jndi-be-gone-1.0.0-standalone.jar` bundles in Byte Buddy. ~~If you
already use Byte Buddy, you may run into issues with it. Try
`log4j-jndi-be-gone-1.0.0.jar` instead, though note that log4j-jndi-be-gone
expects Byte Buddy 1.12.x.~~ As of version 1.1.0, the log4j-jndi-be-gone
standalone JAR bundles a repackaged Byte Buddy under its own package prefix.
This should prevent any collisions.
* If you have replaced your `JndiLookup` classes with implementations that
attempt to do honeypotting or log `lookup()` calls, log4j-jndi-be-gone will
potentially disable their `lookup` method, preventing them from working.
# Example
The `tests/jnditest` directory has a simple test case where a log4j logging
call passes in a JNDI LDAP format string. It also sets up its own port
listener to determine if a connection attempt was made by log4j and fails
the test if a connection was received.
```
$ ./tests/jnditest/test-uninstrumented.sh
BUILD SUCCESSFUL in 1s
6 actionable tasks: 5 executed, 1 up-to-date
BUILD SUCCESSFUL in 1s
3 actionable tasks: 3 up-to-date
JUnit version 4.12
.16:08:49.547 [main] ERROR trust.nccgroup.jnditest.test.JndiTest - Hello, _${jndi:ldap://127.0.0.1:8899/evil}_!
E
Time: 0.929
There was 1 failure:
1) logging(trust.nccgroup.jnditest.test.JndiTest)
java.lang.AssertionError: jndi ldap connection received
at org.junit.Assert.fail(Assert.java:88)
at trust.nccgroup.jnditest.test.JndiTest.logging(JndiTest.java:55)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runners.Suite.runChild(Suite.java:128)
at org.junit.runners.Suite.runChild(Suite.java:27)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runners.Suite.runChild(Suite.java:128)
at org.junit.runners.Suite.runChild(Suite.java:27)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
at org.junit.runner.JUnitCore.runMain(JUnitCore.java:77)
at org.junit.runner.JUnitCore.main(JUnitCore.java:36)
at trust.nccgroup.jnditest.Main.main(Main.java:24)
FAILURES!!!
Tests run: 1, Failures: 1
$ ./tests/jnditest/test-instrumented.sh
BUILD SUCCESSFUL in 1s
6 actionable tasks: 5 executed, 1 up-to-date
BUILD SUCCESSFUL in 1s
3 actionable tasks: 3 up-to-date
JUnit version 4.12
.log4j jndi lookup attempted: (sanitized) ldap://127.0.0.1:8899/evil
16:09:06.064 [main] ERROR trust.nccgroup.jnditest.test.JndiTest - Hello, _(log4j jndi disabled)_!
Time: 1.362
OK (1 test)
```
# License
Licensed under the Apache 2 license.
# Compatability
## Java Versions Tested
log4j-jndi-be-gone has been tested on OpenJDK 6, 8, 11, and 17, and on the HotSpot and OpenJ9 JVMs.
## Log4j Versions Tested
* 2.0
* 2.0.1
* 2.0.2
* 2.1
* 2.2
* 2.3
* 2.4
* 2.4.1
* 2.5
* 2.6
* 2.6.1
* 2.6.2
* 2.7
* 2.8
* 2.8.1
* 2.8.2
* 2.9.0
* 2.9.1
* 2.10.0
* 2.11.0
* 2.11.1
* 2.11.2
* 2.12.0
* 2.12.1
* 2.12.2
* 2.13.0
* 2.13.1
* 2.13.2
* 2.13.3
* 2.14.0
* 2.14.1
* 2.15.0
* 2.16.0
* 2.17.0