CVE-2020-1945: Apache Ant Information Disclosure Flaw

CVE-2020-1945 Overview

Apache Ant versions 1.1 through 1.9.14 and 1.10.0 through 1.10.7 contain an insecure temporary file handling vulnerability that can lead to sensitive information disclosure and build process compromise. The vulnerability arises from Apache Ant's use of the default temporary directory identified by the Java system property java.io.tmpdir for several tasks. This insecure practice allows local attackers to potentially read sensitive data processed during builds. Furthermore, the fixcrlf and replaceregexp tasks copy files from the temporary directory back into the build tree, enabling an attacker to inject modified source files into the build process.

Critical Impact

Local attackers can exploit insecure temporary file handling to leak sensitive build information and inject malicious code into the build process, potentially compromising software integrity.

Affected Products

• Apache Ant 1.1 through 1.9.14
• Apache Ant 1.10.0 through 1.10.7
• Canonical Ubuntu Linux 19.10
• Fedora 31 and 32
• openSUSE Leap 15.2
• Oracle Agile Engineering Data Management 6.2.1.0
• Oracle Banking Enterprise Collections, Liquidity Management, and Platform
• Oracle Business Process Management Suite 12.2.1.3.0 and 12.2.1.4.0
• Oracle Communications ASAP, Diameter Signaling Router, MetaSolv Solution
• Oracle Data Integrator 12.2.1.3.0 and 12.2.1.4.0
• Oracle Primavera Gateway and Unifier (multiple versions)
• Oracle Retail Suite (multiple products and versions)
• Oracle TimesTen In-Memory Database
• Oracle Utilities Framework

Discovery Timeline

• May 14, 2020 - CVE-2020-1945 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-1945

Vulnerability Analysis

This vulnerability (CWE-668: Exposure of Resource to Wrong Sphere) stems from Apache Ant's improper handling of temporary files during build operations. When Ant executes certain tasks, it creates temporary files in the system's default temporary directory without implementing proper access controls or using secure random naming conventions. On multi-user systems, the default temporary directory (typically /tmp on Unix-like systems or %TEMP% on Windows) is world-readable, which means any local user can potentially access files created there.

The vulnerability becomes particularly dangerous because the fixcrlf and replaceregexp tasks not only read from the temporary directory but also copy processed files back into the build tree. This bidirectional file flow creates an opportunity for attackers to plant malicious content in the temporary directory, which then gets incorporated into the legitimate build output. This attack vector could lead to supply chain compromises where malicious code is injected into software during the build process.

Root Cause

The root cause of this vulnerability is the use of the system-wide default temporary directory (java.io.tmpdir) without implementing proper security measures. Apache Ant failed to create task-specific temporary directories with restricted permissions, generate cryptographically random temporary file names to prevent prediction, validate file integrity before copying temporary files back to the build tree, and implement proper file locking mechanisms. This design flaw exposes build artifacts to local attackers who share access to the same temporary directory.

Attack Vector

The attack requires local access to the system where Apache Ant builds are being executed. An attacker positioned on the same system can exploit this vulnerability through the following mechanism:

During an Ant build process, the attacker monitors the default temporary directory for files created by vulnerable Ant tasks. Since the temporary directory is typically world-readable on multi-user systems, the attacker can read sensitive build configuration data, credentials, or source code that Ant processes through temporary files.

For the more severe attack scenario involving code injection, the attacker can predict or race to replace temporary files before the fixcrlf or replaceregexp tasks copy them back to the build directory. By successfully injecting malicious content into these temporary files, the attacker can compromise the integrity of the build output. This could result in backdoored binaries or altered source files being distributed to end users.

Detection Methods for CVE-2020-1945

Indicators of Compromise

• Unexpected files appearing in the system's default temporary directory with patterns matching Ant task temporary file naming
• Modified source files in build directories that differ from version control without corresponding developer changes
• Build output artifacts containing unexpected code or binaries not present in the original source
• Log entries showing unusual file access patterns in /tmp or %TEMP% directories during Ant build execution

Detection Strategies

• Monitor file system activity in the default temporary directory (/tmp, /var/tmp, or %TEMP%) during Ant build processes for suspicious read/write operations by unauthorized users
• Implement file integrity monitoring on build directories to detect unauthorized modifications to source files after build tasks complete
• Audit Apache Ant installation versions across the infrastructure to identify vulnerable deployments running versions prior to 1.9.15 or 1.10.8
• Deploy endpoint detection capabilities to identify race condition exploitation attempts targeting temporary files

Monitoring Recommendations

• Enable detailed logging for Ant build processes to capture all file operations and detect anomalies
• Implement real-time monitoring of build server temporary directories during active build windows
• Configure alerts for any modifications to build output that do not correlate with legitimate source code changes
• Establish baseline file access patterns for build processes to identify deviations indicating potential exploitation

How to Mitigate CVE-2020-1945

Immediate Actions Required

• Upgrade Apache Ant to version 1.9.15 or later (for 1.9.x branch) or version 1.10.8 or later (for 1.10.x branch) immediately
• Review all systems running vulnerable Apache Ant versions and prioritize patching based on exposure and criticality
• Audit recent build outputs from vulnerable systems for signs of tampering or unauthorized modifications
• Restrict access to build servers to minimize the number of local users who could exploit this vulnerability

Patch Information

Apache has released patched versions that address this vulnerability. Users should upgrade to Apache Ant 1.9.15 or later for the 1.9.x release branch, or Apache Ant 1.10.8 or later for the 1.10.x release branch. The patches implement secure temporary file handling with proper access controls and directory isolation. For detailed patch information, refer to the Apache Ant Security Advisory.

Oracle has also released multiple Critical Patch Updates addressing this vulnerability in affected Oracle products. See the Oracle CPU July 2020 and subsequent security alerts for Oracle-specific guidance.

Linux distributions have released updates: Ubuntu Security Notice USN-4380-1, Gentoo GLSA 202007-34, and Fedora package updates are available for affected distributions.

Workarounds

• Configure a dedicated temporary directory with restricted permissions for Ant builds by setting the java.io.tmpdir system property to a secure, non-shared location
• Run Ant builds under dedicated service accounts with isolated home directories and temporary file locations
• Implement build server isolation to prevent local users from accessing the same temporary directories used by build processes
• Use containerized build environments (Docker, Podman) to isolate temporary file operations from other system users

# Configuration example - Set secure temporary directory for Ant builds
# Option 1: Set via ANT_OPTS environment variable
export ANT_OPTS="-Djava.io.tmpdir=/secure/build/tmp"

# Option 2: Create isolated temp directory with restricted permissions
mkdir -p /opt/ant-secure-tmp
chmod 700 /opt/ant-secure-tmp
chown builduser:buildgroup /opt/ant-secure-tmp

# Run Ant with isolated temporary directory
ant -Djava.io.tmpdir=/opt/ant-secure-tmp build