CVE-2026-28208

Junrar is an open source java RAR archive library. Prior to version 7.5.8, a backslash path traversal vulnerability in LocalFolderExtractor allows an attacker to write arbitrary files with attacker-controlled content anywhere on the filesystem when a crafted RAR archive is extracted on Linux/Unix. This can often lead to remote code execution (e.g., overwriting shell profiles, source code, cron jobs, etc). Version 7.5.8 has a fix for the issue.

Junrar is an open source java RAR archive library. Prior to version 7.5.8, a backslash path traversal vulnerability in LocalFolderExtractor allows an attacker to write arbitrary files with attacker-controlled content anywhere on the filesystem when a crafted RAR archive is extracted on Linux/Unix. This can often lead to remote code execution (e.g., overwriting shell profiles, source code, cron jobs, etc). Version 7.5.8 has a fix for the issue.

Summary

A backslash path traversal vulnerability in LocalFolderExtractor allows an attacker to write arbitrary files with attacker-controlled content anywhere on the filesystem when a crafted RAR archive is extracted on Linux/Unix. This can often lead to remote code execution (e.g., overwriting shell profiles, source code, cron jobs, etc).

Details

The createFile() method in LocalFolderExtractor.java validates extraction paths using getCanonicalPath().startsWith() to ensure files stay within the destination directory:

File f = new File(destination, name);
String dirCanonPath = f.getCanonicalPath();
if (!dirCanonPath.startsWith(destination.getCanonicalPath())) {
    throw new IllegalStateException("Rar contains file with invalid path: '" + dirCanonPath + "'");
}

On Linux/Unix, backslashes are literal filename characters, not path separators. A RAR entry named ..\..\tmp\evil.txt is treated by getCanonicalPath() as a single literal filename containing backslash characters — no .. resolution occurs, and the startsWith check passes.

However, makeFile() then splits the filename on backslashes and reconstructs the path using the platform's file separator:

final String[] dirs = name.split("\\\\");
// dirs = ["..", "..", "tmp", "evil.txt"]
// ...
path = path + File.separator + dirs[i];  // File.separator is "/" on Linux

This converts the literal backslashes into real directory traversal: ../../tmp/evil.txt. The extract() method then opens a FileOutputStream on this path and writes the RAR entry's content to it, achieving arbitrary file write outside the extraction directory.

On Windows this is not exploitable because backslashes are path separators, so getCanonicalPath() correctly resolves the .. components and the startsWith check blocks the traversal.

Affected versions: Tested on 7.5.7 (latest). Likely affects all versions that include the makeFile() backslash-splitting logic in LocalFolderExtractor.

PoC (Files Below)

Prerequisites: Linux/Unix system with Java 17+ and Maven installed.

1. Run bash poc_setup.sh which installs junrar 7.5.7 via Maven, creates a malicious RAR archive containing an entry with a backslash-traversal filename (..\..\tmp\existing-file), and creates /tmp/existing-file with the content "Existing File" to simulate a pre-existing file.
2. Run mvn exec:java -Dexec.mainClass='com.test.BackslashTraversalPoC' -q
3. Observe the output shows /tmp/existing-file was overwritten from "Existing File" to "Overwritten", confirming the file outside the extraction directory was written with attacker-controlled content.

The PoC uses Junrar.extract() — the standard public API for extracting RAR archives.

Impact

Any application that extracts user-supplied RAR archives using junrar on Linux/Unix is vulnerable to arbitrary file write/overwrite with attacker-controlled content. This can often lead to RCE.

This affects all Linux/Unix deployments. Windows is not affected.

POC Files

poc_setup.sh

#!/bin/bash
# Setup script for junrar backslash path traversal PoC
# Vulnerability: CWE-22/CWE-29 - Backslash path traversal bypass in LocalFolderExtractor
# Package: com.github.junrar:junrar 7.5.7 (Java)

set -e

# Use the directory where this script lives as the working directory
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
cd "$SCRIPT_DIR"

echo "=== Setting up junrar backslash path traversal PoC ==="
echo "Working directory: $SCRIPT_DIR"

# Clean up artifacts from previous runs
rm -f malicious.rar
rm -rf target extraction-output

# Verify Java and Maven are available
java -version 2>&1 | head -1 || { echo "ERROR: Java not found"; exit 1; }
mvn -version 2>&1 | head -1 || { echo "ERROR: Maven not found"; exit 1; }

# Create Maven project
cat > pom.xml << 'POMEOF'
<?xml version="1.0" encoding="UTF-8"?>
<project…

Junrar is an open source java RAR archive library. Prior to version 7.5.8, a backslash path traversal vulnerability in LocalFolderExtractor allows an attacker to write arbitrary files with attacker-controlled content anywhere on the filesystem when a crafted RAR archive is extracted on Linux/Unix. This can often lead to remote code execution (e.g., overwriting shell profiles, source code, cron jobs, etc). Version 7.5.8 has a fix for the issue.

Junrar is an open source java RAR archive library. Prior to version 7.5.8, a backslash path traversal vulnerability in LocalFolderExtractor allows an attacker to write arbitrary files with attacker-controlled content anywhere on the filesystem when a crafted RAR archive is extracted on Linux/Unix. This can often lead to remote code execution (e.g., overwriting shell profiles, source code, cron jobs, etc). Version 7.5.8 has a fix for the issue.

Summary

A backslash path traversal vulnerability in LocalFolderExtractor allows an attacker to write arbitrary files with attacker-controlled content anywhere on the filesystem when a crafted RAR archive is extracted on Linux/Unix. This can often lead to remote code execution (e.g., overwriting shell profiles, source code, cron jobs, etc).

Details

The createFile() method in LocalFolderExtractor.java validates extraction paths using getCanonicalPath().startsWith() to ensure files stay within the destination directory:

File f = new File(destination, name);
String dirCanonPath = f.getCanonicalPath();
if (!dirCanonPath.startsWith(destination.getCanonicalPath())) {
    throw new IllegalStateException("Rar contains file with invalid path: '" + dirCanonPath + "'");
}

On Linux/Unix, backslashes are literal filename characters, not path separators. A RAR entry named ..\..\tmp\evil.txt is treated by getCanonicalPath() as a single literal filename containing backslash characters — no .. resolution occurs, and the startsWith check passes.

However, makeFile() then splits the filename on backslashes and reconstructs the path using the platform's file separator:

final String[] dirs = name.split("\\\\");
// dirs = ["..", "..", "tmp", "evil.txt"]
// ...
path = path + File.separator + dirs[i];  // File.separator is "/" on Linux

This converts the literal backslashes into real directory traversal: ../../tmp/evil.txt. The extract() method then opens a FileOutputStream on this path and writes the RAR entry's content to it, achieving arbitrary file write outside the extraction directory.

On Windows this is not exploitable because backslashes are path separators, so getCanonicalPath() correctly resolves the .. components and the startsWith check blocks the traversal.

Affected versions: Tested on 7.5.7 (latest). Likely affects all versions that include the makeFile() backslash-splitting logic in LocalFolderExtractor.

PoC (Files Below)

Prerequisites: Linux/Unix system with Java 17+ and Maven installed.

1. Run bash poc_setup.sh which installs junrar 7.5.7 via Maven, creates a malicious RAR archive containing an entry with a backslash-traversal filename (..\..\tmp\existing-file), and creates /tmp/existing-file with the content "Existing File" to simulate a pre-existing file.
2. Run mvn exec:java -Dexec.mainClass='com.test.BackslashTraversalPoC' -q
3. Observe the output shows /tmp/existing-file was overwritten from "Existing File" to "Overwritten", confirming the file outside the extraction directory was written with attacker-controlled content.

The PoC uses Junrar.extract() — the standard public API for extracting RAR archives.

Impact

Any application that extracts user-supplied RAR archives using junrar on Linux/Unix is vulnerable to arbitrary file write/overwrite with attacker-controlled content. This can often lead to RCE.

This affects all Linux/Unix deployments. Windows is not affected.

POC Files

poc_setup.sh

#!/bin/bash
# Setup script for junrar backslash path traversal PoC
# Vulnerability: CWE-22/CWE-29 - Backslash path traversal bypass in LocalFolderExtractor
# Package: com.github.junrar:junrar 7.5.7 (Java)

set -e

# Use the directory where this script lives as the working directory
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
cd "$SCRIPT_DIR"

echo "=== Setting up junrar backslash path traversal PoC ==="
echo "Working directory: $SCRIPT_DIR"

# Clean up artifacts from previous runs
rm -f malicious.rar
rm -rf target extraction-output

# Verify Java and Maven are available
java -version 2>&1 | head -1 || { echo "ERROR: Java not found"; exit 1; }
mvn -version 2>&1 | head -1 || { echo "ERROR: Maven not found"; exit 1; }

# Create Maven project
cat > pom.xml << 'POMEOF'
<?xml version="1.0" encoding="UTF-8"?>
<project…