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// Copyright 2021 Code Intelligence GmbH
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.example;
import com.code_intelligence.jazzer.api.FuzzedDataProvider;
import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.core.Appender;
import org.apache.logging.log4j.core.Core;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.appender.AbstractAppender;
import org.apache.logging.log4j.core.config.Configurator;
import org.apache.logging.log4j.core.config.builder.api.AppenderComponentBuilder;
import org.apache.logging.log4j.core.config.builder.api.RootLoggerComponentBuilder;
import org.apache.logging.log4j.core.config.builder.impl.DefaultConfigurationBuilder;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
import org.apache.logging.log4j.core.config.plugins.PluginFactory;
import org.apache.logging.log4j.core.layout.PatternLayout;
import org.apache.logging.log4j.status.StatusLogger;
// This fuzzer reproduces the log4j RCE vulnerability CVE-2021-44228.
public class Log4jFuzzer {
private final static Logger log = LogManager.getLogger(Log4jFuzzer.class.getName());
public static void fuzzerTestOneInput(FuzzedDataProvider data) {
log.error(data.consumeRemainingAsString());
}
public static void fuzzerInitialize() {
// Install a logger that constructs the log message, but never prints it.
// This noticeably increases the fuzzing performance
DefaultConfigurationBuilder configBuilder = new DefaultConfigurationBuilder();
configBuilder.setPackages(FuzzingAppender.class.getPackage().getName());
AppenderComponentBuilder fuzzingAppender =
configBuilder.newAppender("nullAppender", "FuzzingAppender");
configBuilder.add(fuzzingAppender);
RootLoggerComponentBuilder rootLogger = configBuilder.newRootLogger();
rootLogger.add(configBuilder.newAppenderRef("nullAppender"));
configBuilder.add(rootLogger);
Configurator.reconfigure(configBuilder.build());
// Disable logging of exceptions caught in log4j itself.
StatusLogger.getLogger().reset();
StatusLogger.getLogger().setLevel(Level.OFF);
}
@Plugin(
name = "FuzzingAppender", category = Core.CATEGORY_NAME, elementType = Appender.ELEMENT_TYPE)
public static class FuzzingAppender extends AbstractAppender {
protected FuzzingAppender(String name) {
super(name, null, PatternLayout.createDefaultLayout(), true);
}
@PluginFactory
public static FuzzingAppender createAppender(@PluginAttribute("name") String name) {
return new FuzzingAppender(name);
}
@Override
public void append(LogEvent event) {
try {
getLayout().toByteArray(event);
} catch (Exception ignored) {
// Prevent exceptions from being logged to stderr.
}
}
}
}
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