CVE-2023-20859: Spring Vault Info Disclosure Vulnerability

CVE-2023-20859 Overview

CVE-2023-20859 is an Information Disclosure vulnerability affecting VMware Spring Vault and related Spring Cloud components. The vulnerability allows sensitive information to be inserted into application log files when the application attempts to revoke a Vault batch token. This exposure could allow attackers with local access to log files to obtain sensitive authentication tokens that may still be valid or provide insights into the application's security configuration.

Critical Impact

Sensitive Vault batch tokens may be exposed in log files, potentially enabling unauthorized access to secrets stored in HashiCorp Vault if log files are compromised or accessible to unauthorized parties.

Affected Products

• VMware Spring Vault versions 3.0.x prior to 3.0.2
• VMware Spring Vault versions 2.3.x prior to 2.3.3 and older versions
• VMware Spring Cloud Vault (affected versions)
• VMware Spring Cloud Config (affected versions)

Discovery Timeline

• March 23, 2023 - CVE-2023-20859 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-20859

Vulnerability Analysis

This vulnerability is classified under CWE-532 (Insertion of Sensitive Information into Log File). The issue occurs within Spring Vault's token revocation workflow. When an application using Spring Vault attempts to revoke a Vault batch token, the token value itself is inadvertently written to the application's log files. This behavior violates security best practices as authentication credentials and tokens should never be logged, even during error conditions or debugging scenarios.

The local attack vector requires an attacker to have access to the system's log files, which could occur through various means including compromised log aggregation systems, insufficient file permissions, or insider threats. Once obtained, these tokens could potentially be used to access secrets stored in the Vault instance, depending on the token's permissions and whether it has already been successfully revoked.

Root Cause

The root cause of this vulnerability lies in improper handling of sensitive data during the token revocation process. The Spring Vault library includes the actual token value in log messages rather than masking or omitting this sensitive information. This represents a failure in implementing proper data sanitization before logging operations, which should treat authentication tokens as sensitive data that must never appear in plaintext within log outputs.

Attack Vector

The attack vector for this vulnerability requires local access to the affected system or its log files. An attacker would need to:

1. Gain access to application log files through legitimate means (e.g., system administrator, log aggregation access) or through a separate vulnerability
2. Search log files for exposed Vault batch tokens logged during revocation attempts
3. Attempt to use any discovered tokens before they expire or are successfully revoked

While this is a local attack vector, the impact can be significant in environments where multiple users have access to log files or where logs are stored in centralized logging systems with broad access permissions.

Detection Methods for CVE-2023-20859

Indicators of Compromise

• Presence of Vault batch tokens in application log files in plaintext format
• Unusual access patterns to log files or log aggregation systems
• Authentication attempts to Vault using tokens that should have been revoked
• Unexpected Vault API access patterns from accounts associated with revoked tokens

Detection Strategies

• Implement log file scanning to detect potential token exposure patterns matching Vault token formats
• Monitor Vault audit logs for authentication attempts using tokens that were previously marked for revocation
• Deploy file integrity monitoring on application log directories to detect unauthorized access
• Use SentinelOne Singularity Platform to detect anomalous file access patterns on log directories

Monitoring Recommendations

• Enable comprehensive audit logging on HashiCorp Vault to track all token usage and revocation events
• Implement alerting for authentication attempts using revoked or expired tokens
• Monitor log file access patterns for unusual activity from non-standard processes or users
• Review Spring Vault application logs periodically for signs of sensitive data exposure

How to Mitigate CVE-2023-20859

Immediate Actions Required

• Upgrade Spring Vault to version 3.0.2 or later for the 3.0.x branch
• Upgrade Spring Vault to version 2.3.3 or later for the 2.3.x branch
• Update Spring Cloud Vault and Spring Cloud Config dependencies to patched versions
• Review existing log files for potentially exposed tokens and rotate any credentials that may have been logged
• Restrict access to application log files to essential personnel only

Patch Information

VMware has released patched versions of Spring Vault that address this vulnerability. Organizations should update to Spring Vault 3.0.2 or 2.3.3 depending on their version branch. The patch modifies the logging behavior during token revocation to prevent sensitive token values from being written to log files. For detailed patch information and upgrade instructions, refer to the Spring Security Advisory for CVE-2023-20859.

Workarounds

• Implement strict file permissions on application log directories to limit access to authorized processes and users only
• Configure log rotation and secure deletion policies to minimize the window of exposure for any sensitive data
• Use log filtering or scrubbing solutions to detect and redact patterns matching Vault tokens before log storage
• Consider disabling verbose logging for Vault-related operations until patches can be applied
• Implement network segmentation to limit which systems can access Vault APIs even if tokens are compromised

# Configuration example - Restrict log file permissions
chmod 600 /var/log/spring-vault/*.log
chown app-user:app-group /var/log/spring-vault/*.log

# Configure logrotate with secure deletion
cat >> /etc/logrotate.d/spring-vault << EOF
/var/log/spring-vault/*.log {
    daily
    rotate 7
    compress
    delaycompress
    missingok
    notifempty
    create 600 app-user app-group
    shred
}
EOF