Summary
Using AbstractUnArchiver for extracting an archive might lead to an arbitrary file creation and possibly remote code execution.
Description
When extracting an archive with an entry that already exists in the destination directory as a symbolic link whose target does not exist - the resolveFile() function will return the symlink's source instead of its target, which will pass the verification that ensures the file will not be extracted outside of the destination directory. Later Files.newOutputStream(), that follows symlinks by default, will actually write the entry's content to the symlink's target.
Impact
Whoever uses plexus archiver to extract an untrusted archive is vulnerable to an arbitrary file creation and possibly remote code execution.
Technical Details
In AbstractUnArchiver.java:
protected void extractFile( final File srcF, final File dir, final InputStream compressedInputStream, String entryName, final Date entryDate, final boolean isDirectory, final Integer mode, String symlinkDestination, final FileMapper[] fileMappers)
throws IOException, ArchiverException
{
...
// Hmm. Symlinks re-evaluate back to the original file here. Unsure if this is a good thing...
final File targetFileName = FileUtils.resolveFile( dir, entryName );
// Make sure that the resolved path of the extracted file doesn't escape the destination directory
// getCanonicalFile().toPath() is used instead of getCanonicalPath() (returns String),
// because "/opt/directory".startsWith("/opt/dir") would return false negative.
Path canonicalDirPath = dir.getCanonicalFile().toPath();
Path canonicalDestPath = targetFileName.getCanonicalFile().toPath();
if ( !canonicalDestPath.startsWith( canonicalDirPath ) )
{
throw new ArchiverException( "Entry is outside of the target directory (" + entryName + ")" );
}
try
{
...
if ( !StringUtils.isEmpty( symlinkDestination ) )
{
SymlinkUtils.createSymbolicLink( targetFileName, new File( symlinkDestination ) );
}
else if ( isDirectory )
{
targetFileName.mkdirs();
}
else
{
try ( OutputStream out = Files.newOutputStream( targetFileName.toPath() ) )
{
IOUtil.copy( compressedInputStream, out );
}
}
targetFileName.setLastModified( entryDate.getTime() );
if ( !isIgnorePermissions() && mode != null && !isDirectory )
{
ArchiveEntryUtils.chmod( targetFileName, mode );
}
}
catch ( final FileNotFoundException ex )
{
getLogger().warn( "Unable to expand to file " + targetFileName.getPath() );
}
}
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