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log4shell

Log4Shell Vulnerability

Log4Shell (CVE-2021-44228 and CVE-2021-45046) is a remote-code-execution (RCE) vulnerability, meaning it can force your computer to run any arbitrary Java code.

Anyone can exploit this vulnerability by simply typing a special message into the Minecraft chat.

Log4Shell is caused by certain versions of the Log4j library, which are included in all Minecraft versions from 1.7 (released in 2014) to 1.18 (released in 2021). Both Minecraft clients and Minecraft servers can be vulnerable to this exploit.

Why care?

If you are playing on a Minecraft server and your Minecraft installation is vulnerable (even if the server is patched), then another player could, for example, install a virus on your computer by simply sending you a chat message.1)

Affected versions

Wurst Client

MC VersionStatusPatched byHow to fix
Wurst MC 1.18.1Not affected Relax, you're good. =)
Wurst MC 1.18PatchedFabric Loader 0.12.10, Wurst 7.19Update Wurst or reinstall Fabric.
Wurst MC 1.17.1PatchedFabric Loader 0.12.10, Wurst 7.19Update Wurst or reinstall Fabric.
Wurst MC 1.17PatchedFabric Loader 0.12.10Reinstall Fabric.
Wurst MC 1.16.xPatchedFabric Loader 0.12.10Reinstall Fabric.
Wurst MC 1.15.xPatchedFabric Loader 0.12.10Reinstall Fabric.
Wurst MC 1.14.xPatchedFabric Loader 0.12.10Reinstall Fabric.
Wurst MC 1.12.xPatchedWurst 6.35.2Update Wurst.
ForgeWurst MC 1.12.2PatchedForge 1.12.2-14.23.5.2856Reinstall Forge.
Wurst MC 1.11.xVulnerable Do not use in multiplayer.
ForgeWurst MC 1.11.2Vulnerable Do not use in multiplayer.
Wurst MC 1.10.xVulnerable Do not use in multiplayer.
Wurst MC 1.9.xVulnerable Do not use in multiplayer.
Wurst MC 1.8.xPatchedWurst 6.35.2Update Wurst.
Wurst MC 1.7.xVulnerable Do not use in multiplayer.

Note: Wurst 7.19 and later versions won't even launch when used with a Fabric Loader version older than v0.12.12. This ensures that they cannot accidentally be installed in such a way that they would be vulnerable.

Wolfram Client

MC VersionStatusPatched byHow to fix
Wolfram MC 1.12.xPatchedWolfram 9.8.1Update Wolfram.
Wolfram MC 1.11.xPatchedWolfram 9.8.1Update Wolfram.
Wolfram MC 1.10.xPatchedWolfram 9.8.1Update Wolfram.
Wolfram MC 1.9.4PatchedWolfram 9.8.1Update Wolfram.
Wolfram MC 1.8.xPatchedWolfram 9.8.1Update Wolfram.

Mo Glass

MC VersionStatusPatched byHow to fix
Mo Glass MC 1.18.1Not affected Relax, you're good. =)
Mo Glass MC 1.18PatchedFabric Loader 0.12.10, Mo Glass 1.6Update Mo Glass or reinstall Fabric.
Mo Glass MC 1.17.1PatchedFabric Loader 0.12.10, Mo Glass 1.6Update Mo Glass or reinstall Fabric.
Mo Glass MC 1.17PatchedFabric Loader 0.12.10Reinstall Fabric.
Mo Glass MC 1.16.xPatchedFabric Loader 0.12.10Reinstall Fabric.
Mo Glass MC 1.15.xPatchedFabric Loader 0.12.10Reinstall Fabric.
Mo Glass MC 1.14.xPatchedFabric Loader 0.12.10Reinstall Fabric.

Note: Mo Glass 1.6 and later versions won't even launch when used with a Fabric Loader version older than v0.12.10. This ensures that they cannot accidentally be installed in such a way that they would be vulnerable.

WI Zoom

MC VersionStatusPatched byHow to fix
WI Zoom MC 1.18.1Not affected Relax, you're good. =)
WI Zoom MC 1.18PatchedFabric Loader 0.12.10Reinstall Fabric.
WI Zoom MC 1.17.xPatchedFabric Loader 0.12.10Reinstall Fabric.
WI Zoom MC 1.16.xPatchedFabric Loader 0.12.10Reinstall Fabric.
WI Zoom MC 1.15.xPatchedFabric Loader 0.12.10Reinstall Fabric.
WI Zoom MC 1.14.xPatchedFabric Loader 0.12.10Reinstall Fabric.
WI Zoom MC 1.12.2PatchedForge 1.12.2-14.23.5.2856Reinstall Forge.

How to check your Wurst version

Wurst v7.19 MC1.18.1

Your Wurst version is displayed in the top left corner of the screen.

How to check your Fabric Loader version

Note: Fabric Loader 0.12.12 further improves the Log4Shell patch to cover cases published by CVE-2021-45046. This doesn't affect Minecraft by default, but it is theoretically possible that a mod would enable this issue.

Official Launcher

Click on the “Installations” tab and check what it says under your Fabric installation(s):

Checking the Fabric Loader version in the official Minecraft launcher

MultiMC

Note: MultiMC has released their own patch for the Log4Shell exploit.2) If you are using MultiMC, you might be fine even with a vulnerable version, but you should do a test in singleplayer to be sure.

Click on “Edit Instance” and check what it says next to “Fabric Loader”:

Checking the Fabric Loader version in MultiMC

How to test if you are affected

Open the Minecraft chat and enter the following message:

${jndi:ldap://127.0.0.1/a}

Then check your log file (default: %appdata%/.minecraft/logs/latest.log).

If your Minecraft installation is vulnerable, you will see a a long error like this in the logs:

[17:32:25] [Client thread/INFO]: [CHAT] <Player671> ${jndi:ldap://127.0.0.1/a}
2021-12-11 17:32:29,077 Client thread WARN Error looking up JNDI resource [ldap://127.0.0.1/a]. javax.naming.CommunicationException: 127.0.0.1:389 [Root exception is java.net.ConnectException: Connection refused: connect]
	at com.sun.jndi.ldap.Connection.<init>(Connection.java:243)
	at com.sun.jndi.ldap.LdapClient.<init>(LdapClient.java:137)
	at com.sun.jndi.ldap.LdapClient.getInstance(LdapClient.java:1615)
	at com.sun.jndi.ldap.LdapCtx.connect(LdapCtx.java:2849)
	at com.sun.jndi.ldap.LdapCtx.<init>(LdapCtx.java:347)
	at com.sun.jndi.url.ldap.ldapURLContextFactory.getUsingURLIgnoreRootDN(ldapURLContextFactory.java:60)
	at com.sun.jndi.url.ldap.ldapURLContext.getRootURLContext(ldapURLContext.java:61)
	at com.sun.jndi.toolkit.url.GenericURLContext.lookup(GenericURLContext.java:202)
	at com.sun.jndi.url.ldap.ldapURLContext.lookup(ldapURLContext.java:94)
	at javax.naming.InitialContext.lookup(InitialContext.java:417)
	at org.apache.logging.log4j.core.net.JndiManager.lookup(JndiManager.java:129)
	at org.apache.logging.log4j.core.lookup.JndiLookup.lookup(JndiLookup.java:54)
	at org.apache.logging.log4j.core.lookup.Interpolator.lookup(Interpolator.java:183)
	at org.apache.logging.log4j.core.lookup.StrSubstitutor.resolveVariable(StrSubstitutor.java:1054)
	at org.apache.logging.log4j.core.lookup.StrSubstitutor.substitute(StrSubstitutor.java:976)
	at org.apache.logging.log4j.core.lookup.StrSubstitutor.substitute(StrSubstitutor.java:872)
	at org.apache.logging.log4j.core.lookup.StrSubstitutor.replace(StrSubstitutor.java:427)
	at org.apache.logging.log4j.core.pattern.MessagePatternConverter.format(MessagePatternConverter.java:127)
	at org.apache.logging.log4j.core.pattern.PatternFormatter.format(PatternFormatter.java:38)
	at org.apache.logging.log4j.core.layout.PatternLayout$PatternSerializer.toSerializable(PatternLayout.java:333)
	at org.apache.logging.log4j.core.layout.PatternLayout.toText(PatternLayout.java:232)
	at org.apache.logging.log4j.core.layout.PatternLayout.encode(PatternLayout.java:217)
	at org.apache.logging.log4j.core.layout.PatternLayout.encode(PatternLayout.java:57)
	at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.directEncodeEvent(AbstractOutputStreamAppender.java:177)
	at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.tryAppend(AbstractOutputStreamAppender.java:170)
	at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.append(AbstractOutputStreamAppender.java:161)
	at org.apache.logging.log4j.core.appender.RollingRandomAccessFileAppender.append(RollingRandomAccessFileAppender.java:218)
	at org.apache.logging.log4j.core.config.AppenderControl.tryCallAppender(AppenderControl.java:156)
	at org.apache.logging.log4j.core.config.AppenderControl.callAppender0(AppenderControl.java:129)
	at org.apache.logging.log4j.core.config.AppenderControl.callAppenderPreventRecursion(AppenderControl.java:120)
	at org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:84)
	at org.apache.logging.log4j.core.config.LoggerConfig.callAppenders(LoggerConfig.java:448)
	at org.apache.logging.log4j.core.config.LoggerConfig.processLogEvent(LoggerConfig.java:433)
	at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:417)
	at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:403)
	at org.apache.logging.log4j.core.config.AwaitCompletionReliabilityStrategy.log(AwaitCompletionReliabilityStrategy.java:63)
	at org.apache.logging.log4j.core.Logger.logMessage(Logger.java:146)
	at org.apache.logging.log4j.spi.AbstractLogger.logMessageSafely(AbstractLogger.java:2091)
	at org.apache.logging.log4j.spi.AbstractLogger.logMessage(AbstractLogger.java:2005)
	at org.apache.logging.log4j.spi.AbstractLogger.logIfEnabled(AbstractLogger.java:1876)
	at org.apache.logging.log4j.spi.AbstractLogger.info(AbstractLogger.java:1421)
	at net.minecraft.client.gui.GuiNewChat.printChatMessageWithOptionalDeletion(GuiNewChat.java:157)
	at net.minecraft.client.gui.GuiNewChat.printChatMessage(GuiNewChat.java:140)
	at net.minecraft.client.gui.chat.NormalChatListener.func_192576_a(NormalChatListener.java:18)
	at net.minecraft.client.gui.GuiIngame.func_191742_a(GuiIngame.java:1319)
	at net.minecraft.client.network.NetHandlerPlayClient.handleChat(NetHandlerPlayClient.java:813)
	at net.minecraft.network.play.server.SPacketChat.processPacket(SPacketChat.java:53)
	at net.minecraft.network.play.server.SPacketChat.processPacket(SPacketChat.java:1)
	at net.minecraft.network.PacketThreadUtil$1.run(PacketThreadUtil.java:15)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at net.minecraft.util.Util.runTask(Util.java:47)
	at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:1133)
	at net.minecraft.client.Minecraft.run(Minecraft.java:428)
	at net.minecraft.client.main.Main.main(Main.java:115)
	at Start.main(Start.java:11)
Caused by: java.net.ConnectException: Connection refused: connect
	at java.net.DualStackPlainSocketImpl.connect0(Native Method)
	at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
	at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
	at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
	at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
	at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
	at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
	at java.net.Socket.connect(Socket.java:607)
	at java.net.Socket.connect(Socket.java:556)
	at java.net.Socket.<init>(Socket.java:452)
	at java.net.Socket.<init>(Socket.java:229)
	at com.sun.jndi.ldap.Connection.createSocket(Connection.java:380)
	at com.sun.jndi.ldap.Connection.<init>(Connection.java:220)
	... 55 more

If your Minecraft installation is not vulnerable, you will simply see the chat message in the logs:

[17:37:50] [Server thread/INFO]: <Player578> ${jndi:ldap://127.0.0.1/a}
[17:37:50] [Client thread/INFO]: [CHAT] <Player578> ${jndi:ldap://127.0.0.1/a}
1)
They could also install DOOM instead, but most attackers would probably choose malware.
log4shell.txt · Last modified: 2022/01/20 07:55 by alexander01998

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