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April 20, 2022

GHSL-2022-012: Arbitrary file write during TAR extraction in Apache Hadoop - CVE-2022-26612

Jaroslav Lobacevski

Coordinated Disclosure Timeline

Summary

Function unpackEntries during TAR extraction follows symbolic links (symlinks) which allows writing outside expected base directory on Windows.

Product

Apache Hadoop

Tested Version

Latest version from the trunk

Details

Issue: arbitrary file write in unpackEntries on Windows (GHSL-2022-012)

unTar uses unTarUsingJava function on Windows and the built-in tar utility on Unix and other OSes:

if(Shell.WINDOWS) {
  // Tar is not native to Windows. Use simple Java based implementation for
  // tests and simple tar archives
  unTarUsingJava(inFile, untarDir, gzipped);
}
else {
  // spawn tar utility to untar archive for full fledged unix behavior such
  // as resolving symlinks in tar archives
  unTarUsingTar(inFile, untarDir, gzipped);
}

The function verifies that the extracted TAR entry is under the expected targetDirPath:

if (!outputFile.getCanonicalPath().startsWith(targetDirPath)) {
  throw new IOException("expanding " + entry.getName()
      + " would create entry outside of " + outputDir);
}

However it doesn’t apply the same restriction to the target of an extracted symlink:

if (entry.isSymbolicLink()) {
  // Create symbolic link relative to tar parent dir
  Files.createSymbolicLink(FileSystems.getDefault()
          .getPath(outputDir.getPath(), entry.getName()),
      FileSystems.getDefault().getPath(entry.getLinkName())); //<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
  return;
}

As a result a TAR entry may create a symlink under the expected extraction directory which points to an external directory. A subsequent TAR entry may extract an arbitrary file into the external directory using the symlink name. This however would be caught by the same targetDirPath check on Unix because of the getCanonicalPath call. However on Windows getCanonicalPath doesn’t resolve symbolic links, which bypasses the check.

Note: In general, creation of symlinks on Windows requires elevated privileges that are not granted to standard users. The privilege can be granted to standard users per SeCreateSymbolicLinkPrivilege or to all users globally if Developer Mode is enabled.

Impact

This issue allows arbitrary write outside the expected extraction directory on Windows.

CVE

Credit

This issue was discovered and reported by GHSL team member @JarLob (Jaroslav Lobačevski).

Contact

You can contact the GHSL team at securitylab@github.com, please include a reference to GHSL-2022-012 in any communication regarding this issue.