CVE-2020-17521: Apache Groovy Insecure Temp File Flaw

CVE-2020-17521 Overview

Apache Groovy provides extension methods to aid with creating temporary directories. Prior to the fix, Groovy's implementation of those extension methods was using a now superseded Java JDK method call that is potentially not secure on some operating systems in certain contexts. This vulnerability affects users who utilize the temporary directory extension methods in Groovy, potentially exposing sensitive data to local attackers through insecure temporary file handling.

Critical Impact

Local attackers with access to the system may be able to read sensitive information stored in temporary directories created by vulnerable Groovy applications due to insecure default permissions.

Affected Products

• Apache Groovy versions 2.0 to 2.4.20
• Apache Groovy versions 2.5.0 to 2.5.13
• Apache Groovy versions 3.0.0 to 3.0.6
• Apache Groovy version 4.0.0-alpha-1
• NetApp SnapCenter
• Oracle Agile Engineering Data Management 6.2.1.0
• Oracle Agile PLM 9.3.3 and 9.3.6
• Oracle Business Process Management Suite 12.2.1.3.0 and 12.2.1.4.0
• Oracle Communications products (BRM Elastic Charging Engine, Diameter Signaling Router, ECAS, Services Gatekeeper)
• Oracle Primavera Gateway and Primavera Unifier
• Oracle Retail products (Bulk Data Integration, Merchandising System, Store Inventory Management)
• Apache Atlas 2.1.0

Discovery Timeline

• December 7, 2020 - CVE-2020-17521 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-17521

Vulnerability Analysis

The vulnerability exists in Apache Groovy's temporary directory creation extension methods. These methods relied on deprecated Java JDK APIs that do not properly secure temporary files and directories on certain operating systems. When applications use Groovy's extension methods like File.createTempDir(), the created directories may have overly permissive default permissions, allowing other local users on the system to access, read, or potentially modify files within these temporary directories.

The issue is particularly concerning on multi-user systems or shared hosting environments where multiple users or processes may have access to the system's temporary directory locations (typically /tmp on Unix-like systems or %TEMP% on Windows). The underlying Java method used by Groovy did not atomically set restrictive permissions on the created directory, creating a race condition window where other users could access the directory contents.

Root Cause

The root cause of this vulnerability is the use of superseded Java JDK method calls for temporary directory creation that do not implement secure default permissions. The deprecated methods in Java's File class used by Groovy do not atomically create directories with restrictive access permissions. Instead, they create directories with default system permissions, which on many systems allow read access to all users. Modern Java versions provide java.nio.file.Files.createTempDirectory() which properly sets restrictive permissions atomically, preventing the race condition and information disclosure.

Attack Vector

The attack requires local access to the target system. An attacker with a valid account on the same system as the vulnerable application can exploit this vulnerability by monitoring the system's temporary directory location for newly created directories. When a Groovy application creates a temporary directory using the vulnerable extension methods, the attacker can access the directory and read any sensitive data written there before the application completes its operations.

The exploitation scenario involves:

1. Attacker gains local access to a system running a Groovy application
2. Attacker monitors the temporary directory for new directory creation
3. Vulnerable Groovy application creates temporary directory with default (permissive) permissions
4. Attacker accesses the temporary directory and exfiltrates sensitive data

Since no verified proof-of-concept code is available, the vulnerability can be understood conceptually: applications using ResourceGroovyMethods.createTempDir() or similar extension methods would create directories readable by other local users, potentially exposing configuration files, credentials, or other sensitive application data written to temporary storage.

Detection Methods for CVE-2020-17521

Indicators of Compromise

• Unexpected access to application temporary directories by non-application users
• Log entries showing file access or permission errors in temporary directories
• Anomalous user activity in /tmp or system temporary directory locations
• Process monitoring tools showing unauthorized access to Groovy application temp files

Detection Strategies

• Audit Groovy library versions in deployed applications using software composition analysis (SCA) tools
• Monitor file system access events to temporary directories using audit frameworks (auditd on Linux)
• Implement application-level logging for temporary file creation and access patterns
• Use endpoint detection tools to identify processes accessing temp directories created by other users

Monitoring Recommendations

• Enable file integrity monitoring on temporary directory locations used by critical applications
• Configure SIEM rules to alert on cross-user temporary file access patterns
• Implement periodic vulnerability scanning to identify outdated Groovy dependencies
• Monitor for updates to Oracle, NetApp, and other vendor security advisories addressing this CVE

How to Mitigate CVE-2020-17521

Immediate Actions Required

• Upgrade Apache Groovy to fixed versions: 2.4.21, 2.5.14, 3.0.7, or 4.0.0-alpha-2 or later
• Review applications for usage of temporary directory extension methods and assess exposure
• Apply vendor patches from Oracle, NetApp, and other affected product vendors
• Restrict local system access to minimize attack surface for local privilege escalation
• Implement application-level controls to set restrictive permissions on temporary directories

Patch Information

Apache Groovy has released patched versions that address this vulnerability by using secure temporary directory creation methods. The fixed versions are:

• Apache Groovy 2.4.21 (for 2.x legacy branch)
• Apache Groovy 2.5.14 (for 2.5.x branch)
• Apache Groovy 3.0.7 (for 3.x branch)
• Apache Groovy 4.0.0-alpha-2 (for 4.x development branch)

For downstream products, refer to vendor advisories:

• Oracle Security Alert CPU January 2021
• Oracle Security Alert CPU April 2021
• Oracle Security Alert CPU July 2021
• NetApp Security Advisory NTAP-20201218-0006
• Groovy Security Advisory CVE-2020-17521

Workarounds

• Avoid using Groovy's temporary directory extension methods until patching is possible
• Implement custom temporary directory creation using java.nio.file.Files.createTempDirectory() which sets secure permissions
• Set restrictive umask values at the application or system level to limit default permissions
• Use dedicated temporary directories with pre-configured restrictive permissions for sensitive applications
• Isolate applications handling sensitive data in containers or VMs to reduce local attack surface

# Set restrictive umask for Groovy applications (Unix/Linux)
umask 077

# Verify temporary directory permissions
ls -la /tmp | grep your_app_temp_dir

# Check Groovy version in your application
groovy --version