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https://issues.apache.org/jira/browse/FILEUPLOAD-279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16684646#comment-16684646
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Bernd Eckenfels commented on FILEUPLOAD-279:
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This is not (directly) related to Struts.
The DiskFileItem class lingers around in your applications and this adds a
trivial Widget to be exploited by serialisation attacks. It might not be the
only vector, and deserialising untrusted data is fatal in itself, hoewever you
would still be guilty of not having updated a class with known vulnerabilities.
So just update.
if you cant update (for whatever reason) then the only thing to mitigate you
can do is to actually review all usage of serialisation in your apps. You
should probably do that anyway.
it might be possible that you notice upload_uuid_id.tmp file in random
directories, but they do only show up for short times if it is used to generate
files.
I would better like to understand why can’t people just upgrade, is there
something we can make it easier?
> CVE-2016-1000031 - Apache Commons FileUpload DiskFileItem File Manipulation
> Remote Code Execution
> -------------------------------------------------------------------------------------------------
>
> Key: FILEUPLOAD-279
> URL: https://issues.apache.org/jira/browse/FILEUPLOAD-279
> Project: Commons FileUpload
> Issue Type: Bug
> Affects Versions: 1.3.2
> Reporter: Michiel Weggen
> Priority: Critical
> Labels: security
> Fix For: 1.3.3
>
> Attachments: fix2.patch
>
>
> http://www.tenable.com/security/research/tra-2016-12
> Summary
> There exists a Java Object in the Apache Commons FileUpload library that can
> be manipulated in such a way that when it is deserialized, it can write or
> copy files to disk in arbitrary locations. Furthermore, while the Object can
> be used alone, this new vector can be integrated with ysoserial to upload and
> execute binaries in a single deserialization call. This may or may not work
> depending on an application's implementation of the FileUpload library.
> Background
> In late 2015 FoxGlove Security released a write up on using Chris Frohoff’s
> yososerial tool to gain remote code execution on a variety of commercial
> products, based on a presentation at AppSec Cali in January, 2015. The
> ysoserial tool uses “gadgets” in Apache Commons Collections, Groovy, and
> Spring that do “unexpected” things during deserialization. Specifically, the
> ysoserial payloads eventually execute Runtime.getRuntime().exec() allowing
> for remote Java code execution.
> The Apache Commons project maintains a library called “FileUpload” to make
> “it easy to add robust, high-performance, file upload capability to your
> servlets and web applications.” One of the classes in the FileUpload library
> is called “DiskFileItem”. A DiskFileItem is used to handle file uploads.
> Interestingly, DiskFileItem is serializable and implements custom
> writeObject() and readObject() functions.
> DiskFileItem’s readObject Implementation
> Here is the implementation that currently exists at the projects repository
> tip (as of 1/28/16):
> 632 private void readObject(ObjectInputStream in)
> 633 throws IOException, ClassNotFoundException {
> 634 // read values
> 635 in.defaultReadObject();
> 636
> 637 /* One expected use of serialization is to migrate HTTP sessions
> 638 * containing a DiskFileItem between JVMs. Particularly if the
> JVMs are
> 639 * on different machines It is possible that the repository
> location is
> 640 * not valid so validate it.
> 641 */
> 642 if (repository != null) {
> 643 if (repository.isDirectory()) {
> 644 // Check path for nulls
> 645 if (repository.getPath().contains("\0")) {
> 646 throw new IOException(format(
> 647 "The repository [%s] contains a null
> character",
> 648 repository.getPath()));
> 649 }
> 650 } else {
> 651 throw new IOException(format(
> 652 "The repository [%s] is not a directory",
> 653 repository.getAbsolutePath()));
> 654 }
> 655 }
> 656
> 657 OutputStream output = getOutputStream();
> 658 if (cachedContent != null) {
> 659 output.write(cachedContent);
> 660 } else {
> 661 FileInputStream input = new FileInputStream(dfosFile);
> 662 IOUtils.copy(input, output);
> 663 IOUtils.closeQuietly(input);
> 664 dfosFile.delete();
> 665 dfosFile = null;
> 666 }
> 667 output.close();
> 668
> 669 cachedContent = null;
> 670 }
> This is interesting due to the apparent creation of files. However, after
> analyzing the state of DiskFileItem after serialization it became clear that
> arbitrary file creation was not supposed to be intended:
> dfos (a type of OutputStream) is transient and therefore it is not
> serialized. dfos is regenerated by the getOutputStream() call above (which
> also generates the new File to write out to).
> The “repository” (or directory that the file is written to) has to be valid
> at the time of serialization in order for successful deserialization to occur.
> If there is no “cachedContent” then readObject() tries to read in the file
> from disk.
> That filename is always generated via getOutputStream.
> Serialized Object Modification
> The rules listed above do not take into account that someone might modify the
> serialized data before it is deserialized. Three important elements get
> serialized that we can modify:
> The repository path (aka the directory that the file is read/written from).
> If there is cachedContent (i.e. data that didn’t get written to the file)
> then that gets serialized
> If there is no cachedContent (i.e. all data was written to disk) the full
> path to the output file exists.
> The threshold value that controls if “cachedContent” is written to disk or
> not.
> Modifying these three elements in the serialized object gives us the ability
> to:
> Create files wherever we have permission on the system. The caveat here is
> that we only have control of the file path and not the final filename.
> Copy the contents of files from one file on the system to a location we
> specify (again we only control the directory path and not the filename). This
> will also attempt to delete the file we copy from.. so be careful.
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