A tool to dump and rebuild Java serialization streams and Java RMI packet contents in a more human readable form.
The tool does not deserialize the stream (i.e. objects in the stream are not instantiated), so it does not require access to the classes that were used in the stream*.
This tool was developed to support research into Java deserialization vulnerabilities after spending many hours manually decoding raw serialization streams to debug code!
Download v1.1 built and ready to run from here: https://github.com/NickstaDB/SerializationDumper/releases/download/1.1/SerializationDumper-v1.1.jar
* See the limitations section below for more details.
Update 19/12/2018: SerializationDumper now supports rebuilding serialization streams so you can dump a Java serialization stream to a text file, modify the hex or string values, then convert the text file back into a binary serialization stream. See the section below on Rebuilding Serialization Streams for an example of this.
build.bat to compile the JAR from the latest sources.
SerializationDumper can take input in the form of hex-ascii encoded bytes on the command line, hex-ascii encoded bytes in a file, or a file containing raw serialized data. The following examples demonstrate its use:
$ java -jar SerializationDumper-v1.1.jar aced0005740004414243447071007e0000 STREAM_MAGIC - 0xac ed STREAM_VERSION - 0x00 05 Contents TC_STRING - 0x74 newHandle 0x00 7e 00 00 Length - 4 - 0x00 04 Value - ABCD - 0x41424344 TC_NULL - 0x70 TC_REFERENCE - 0x71 Handle - 8257536 - 0x00 7e 00 00 $ java -jar SerializationDumper-v1.1.jar -f hex-ascii-input-file.txt STREAM_MAGIC - 0xac ed STREAM_VERSION - 0x00 05 Contents TC_NULL - 0x70 $ java -jar SerializationDumper-v1.1.jar -r raw-input-file.bin STREAM_MAGIC - 0xac ed STREAM_VERSION - 0x00 05 Contents TC_CLASSDESC - 0x72 className Length - 11 - 0x00 0b Value - com.foo.Bar - 0x636f6d2e666f6f2e426172 serialVersionUID - 0x01 02 03 04 05 06 07 08 newHandle 0x00 7e 00 00 classDescFlags - 0x02 - SC_SERIALIZABLE fieldCount - 0 - 0x00 00 classAnnotations TC_ENDBLOCKDATA - 0x78 superClassDesc TC_NULL - 0x70
Rebuilding Serialization Streams
As of 19/12/2018, SerializationDumper can do the reverse operation and convert a dumped serialization stream back into a raw byte stream. This can be useful for working with raw serialized streams because modifications can be made to the dumped text and be "recompiled" back into a byte stream.
To demonstrate the use of the stream rebuilding functionality, let's start with a simple serialization stream.
We can dump this using SerializationDumper, as shown above, to get the following:
STREAM_MAGIC - 0xac ed STREAM_VERSION - 0x00 05 Contents TC_STRING - 0x74 newHandle 0x00 7e 00 00 Length - 4 - 0x00 04 Value - ABCD - 0x41424344 TC_NULL - 0x70 TC_REFERENCE - 0x71 Handle - 8257536 - 0x00 7e 00 00
To modify the string value from
AAAABBBB we must update the hex-ascii values for both the string length and the string value as follows:
STREAM_MAGIC - 0xac ed STREAM_VERSION - 0x00 05 Contents TC_STRING - 0x74 newHandle 0x00 7e 00 00 Length - 4 - 0x00 08 Value - ABCD - 0x4141414142424242 TC_NULL - 0x70 TC_REFERENCE - 0x71 Handle - 8257536 - 0x00 7e 00 00
If we save this to the file
dumped.txt then we can rebuild the stream as follows:
$ java -jar SerializationDumper-v1.1.jar -b dumped.txt rebuilt.bin
rebuilt.bin will now contain the raw bytes of the modified serialization stream. If we encode that file as hex-ascii we get the following:
See the limitations section below for stream rebuilding limitations.
The tool cannot deserialize all Java serialized data streams and may not be fully compliant with the Java serialization specification. In particular, if the stream contains an externalContents element then it cannot be deserialized without using the original class. If you have something that cannot be dumped which does not include an
externalContents element then please get in touch with some sample data so I can look at producing a fix!
externalContents: If a class implements the interface
java.io.Externalizable then it can use the
writeExternal method to write custom data to the serialization stream. This data can only be parsed by the corresponding
readExternal method so it is not possible to read the data without access to the original class. Such classes will have the
SC_EXTERNALIZABLE flag set in the
classDescFlags field but they will not have the
SC_BLOCKDATA flag set.
###Serialization/Rebuild Mode The stream rebuild mode currently only operates on the hex-ascii encoded bytes from the dumped data. For that reason, changing the string "ABCD" to "AAAABBBB" won't have the desired effect of producing the bytes 0x4141414142424242 in the output file. A future update may improve this but for now you'll have to do your hex-ascii encoding of strings manually!
Length fields aren't updated automatically during stream rebuilding. This may be desirable or not, but if you modify a string value in a way that changes the length just be aware that you may also need to modify the length (hex-ascii) field accordingly. The same applies to arrays.
If the stream contains any
TC_REFERENCE elements and you modify it to remove an element that includes a
newHandle field then you may break the references in the stream unless you manually update them. Reference handles/IDs are incremental and start at
0x7e0000 so the first
newHandle field is reference by
0x7e0000, the second by
0x7e0001, and so on. If the first element with a
newHandle field is removed from the stream then any
TC_REFERENCE elements in the stream must be modified to refer to a handle value one less than what they originally referred to.
This tool was hacked together on the fly to support my own research but if you find the tool useful and have any bug reports or suggestions please get in touch either here or on Twitter (@NickstaDB).