Introduced protections against "zip slip" attacks

[pixeebot]

This change updates all new instances of ZipInputStream to protect against malicious entries that attempt to escape their "file root" and overwrite other files on the running filesystem.

Normally, when you're using ZipInputStream it's because you're processing zip files. That code might look like this:

File file = new File(unzipTargetDirectory, zipEntry.getName()); // use file name from zip entry
InputStream is = zip.getInputStream(zipEntry); // get the contents of the zip entry
IOUtils.copy(is, new FileOutputStream(file)); // write the contents to the provided file name

This looks fine when it encounters a normal zip entry within a zip file, looking something like this pseudo-data:

path: data/names.txt
contents: Zeus\nHelen\nLeda...

However, there's nothing to prevent an attacker from sending an evil entry in the zip that looks more like this:

path: ../../../../../etc/passwd
contents: root::0:0:root:/:/bin/sh

Yes, in the above code, which looks like every piece of zip-processing code you can find on the Internet, attackers could overwrite any files to which the application has access. This rule replaces the standard ZipInputStream with a hardened subclass which prevents access to entry paths that attempt to traverse directories above the current directory (which no normal zip file should ever do.) Our changes end up looking something like this:

+ import io.github.pixee.security.ZipSecurity;
  ...
- var zip = new ZipInputStream(is, StandardCharsets.UTF_8);
+ var zip = ZipSecurity.createHardenedInputStream(is, StandardCharsets.UTF_8);

❌ The following packages couldn't be installed automatically, probably because the dependency manager is unsupported. Please install them manually:

Gradle

dependencies {
  implementation("io.github.pixee:java-security-toolkit:1.2.0")
}

Maven

<dependencies>
  <dependency>
    <groupId>io.github.pixee</groupId>
    <artifactId>java-security-toolkit</artifactId>
    <version>1.2.0</version>
  </dependency>
<dependencies>

More reading

• https://snyk.io/research/zip-slip-vulnerability
• https://github.com/snyk/zip-slip-vulnerability
• https://wiki.sei.cmu.edu/confluence/display/java/IDS04-J.+Safely+extract+files+from+ZipInputStream
• https://vulncat.fortify.com/en/detail?id=desc.dataflow.java.path_manipulation_zip_entry_overwrite

I have additional improvements ready for this repo! If you want to see them, leave the comment:

@pixeebot next

... and I will open a new PR right away!

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Feedback | Community | Docs | Codemod ID: pixee:java/harden-zip-entry-paths

[pixeebot]

I'm confident in this change, but I'm not a maintainer of this project. Do you see any reason not to merge it?

If this change was not helpful, or you have suggestions for improvements, please let me know!

[pixeebot]

This change shouldn't have any effect on normal unzipping operations -- it should only throw a SecurityException if it operates on a maliciously created zip.

If there are other concerns about this change, I'd love to hear about them!

[pixeebot]

This change may not be a priority right now, so I'll close it. If there was something I could have done better, please let me know!

You can also customize me to make sure I'm working with you in the way you want.