Java "internal_error" with MITM on some sites

[jekh]

A BrowserMob Proxy user reported an issue where sites using the CloudFlare Flexible SSL service, such as https://kitematic.com/, experience this error:

Caused by: javax.net.ssl.SSLException: Received fatal alert: internal_error

I traced this problem back to LittleProxy, but I'm at a loss to understand what "internal_error" could possibly mean. Does anybody with more experience with Java SSL have any ideas what might be causing this?

Full LP log output:

0      2015-05-16 21:12:03,879 INFO  [main] proxy.Launcher (?:?).?() - Running LittleProxy with args: []
About to start server on port: 8080
91     2015-05-16 21:12:03,970 INFO  [main] proxy.Launcher (?:?).?() - Running as Man in the Middle
92     2015-05-16 21:12:03,971 INFO  [main] extras.SelfSignedSslEngineSource (?:?).?() - Not deleting keystore
About to start...
212    2015-05-16 21:12:04,091 INFO  [main] impl.DefaultHttpProxyServer (?:?).?() - Starting proxy at address: 0.0.0.0/0.0.0.0:8080
233    2015-05-16 21:12:04,112 INFO  [main] impl.DefaultHttpProxyServer (?:?).?() - Proxy listening with TCP transport
305    2015-05-16 21:12:04,184 INFO  [main] impl.DefaultHttpProxyServer (?:?).?() - Proxy started at address: /0:0:0:0:0:0:0:0:8080
18878  2015-05-16 21:12:22,757 WARN  [LittleProxy-ProxyToServerWorker-0] impl.ProxyToServerConnection (?:?).?() - (HANDSHAKING) [id: 0x5d8ce589, 0.0.0.0/0.0.0.0:46433 :> kitematic.com/104.28.2.49:443]: Caught exception on proxy -> web connection
io.netty.handler.codec.DecoderException: javax.net.ssl.SSLException: Received fatal alert: internal_error
    at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:280)
    at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:149)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:333)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:319)
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:787)
    at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:130)
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:511)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:468)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:382)
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:354)
    at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116)
    at java.lang.Thread.run(Thread.java:745)
Caused by: javax.net.ssl.SSLException: Received fatal alert: internal_error
    at sun.security.ssl.Alerts.getSSLException(Alerts.java:208)
    at sun.security.ssl.SSLEngineImpl.fatal(SSLEngineImpl.java:1650)
    at sun.security.ssl.SSLEngineImpl.fatal(SSLEngineImpl.java:1618)
    at sun.security.ssl.SSLEngineImpl.recvAlert(SSLEngineImpl.java:1787)
    at sun.security.ssl.SSLEngineImpl.readRecord(SSLEngineImpl.java:1071)
    at sun.security.ssl.SSLEngineImpl.readNetRecord(SSLEngineImpl.java:893)
    at sun.security.ssl.SSLEngineImpl.unwrap(SSLEngineImpl.java:767)
    at javax.net.ssl.SSLEngine.unwrap(SSLEngine.java:624)
    at io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:982)
    at io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:908)
    at io.netty.handler.ssl.SslHandler.decode(SslHandler.java:854)
    at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:249)
    ... 11 more
18880  2015-05-16 21:12:22,759 WARN  [LittleProxy-ProxyToServerWorker-0] impl.ProxyToServerConnection (?:?).?() - (HANDSHAKING) [id: 0x5d8ce589, 0.0.0.0/0.0.0.0:46433 :> kitematic.com/104.28.2.49:443]: Disconnecting open connection

[ganskef]

Hi Jason, I've reproduced it with https://kitematic.com/ (with my implementation and Netty 4.1.0-Beta5), too. I've ececuted my tests with -Djavax.net.debug=all and compare a direct with a proxied connection. I've found this difference in the output:

Working handshake with URLConnection
*** ClientHello, TLSv1
...
Extension elliptic_curves, curve names: {secp256r1, secp384r1, secp521r1}
Extension ec_point_formats, formats: [uncompressed]
Extension server_name, server_name: [host_name: kitematic.com]

---

Failing handshake with LittleProxy
*** ClientHello, TLSv1
...
Extension elliptic_curves, curve names: {secp256r1, secp384r1, secp521r1}
Extension ec_point_formats, formats: [uncompressed]

---

Stay tuned...

[jekh]

Thanks for investigating this, @ganskef. I just opened PR #210 with the commit you referenced here. Would you mind taking a look and letting me know if there's anything else that needs to be done before this can be merged?

This is actually a major issue, so thank you so much for investigating & fixing it!

[jekh]

Since the discussion is taking place in PR #210 now, I'll close this issue.