CVE-2026-24308: Apache ZooKeeper Information Disclosure

CVE-2026-24308 Overview

CVE-2026-24308 is an information disclosure vulnerability affecting Apache ZooKeeper versions 3.8.5 and 3.9.4 across all platforms. The vulnerability stems from improper handling of configuration values in the ZKConfig component, which causes sensitive information stored in client configuration to be exposed through client logfiles. Configuration values are logged at INFO level, potentially affecting production systems where log aggregation and retention may expose credentials or other sensitive configuration data to unauthorized parties.

Critical Impact

Sensitive configuration values including potential credentials and connection strings may be exposed through client logfiles at INFO logging level, enabling attackers with log access to harvest sensitive data from production ZooKeeper deployments.

Affected Products

• Apache ZooKeeper 3.8.5
• Apache ZooKeeper 3.9.4
• All platforms running the affected versions

Discovery Timeline

• 2026-03-07 - CVE-2026-24308 published to NVD
• 2026-03-10 - Last updated in NVD database

Technical Details for CVE-2026-24308

Vulnerability Analysis

This vulnerability is classified under CWE-532 (Insertion of Sensitive Information into Log File), a common security weakness where applications inadvertently write sensitive data to log files. In the case of CVE-2026-24308, the ZKConfig component in Apache ZooKeeper fails to properly sanitize or mask configuration values before logging them.

When ZooKeeper clients initialize or reload configuration, the ZKConfig module logs configuration values at the INFO level. This behavior is problematic because INFO-level logging is typically enabled in production environments for operational monitoring. As a result, sensitive information such as authentication credentials, connection strings, encryption keys, or other confidential configuration parameters may be written to log files in plaintext.

The network-accessible nature of this vulnerability means that attackers who gain access to log files—whether through log aggregation systems, backup storage, or direct file system access—can harvest sensitive configuration data without needing to interact with the ZooKeeper service directly.

Root Cause

The root cause of CVE-2026-24308 lies in the ZKConfig component's logging implementation. The component logs configuration values at INFO level without implementing proper filtering or masking mechanisms for sensitive parameters. This design flaw results in configuration values being written directly to client logfiles regardless of their sensitivity.

Proper secure logging practices dictate that sensitive configuration values should either be excluded from logs entirely, masked with placeholder characters, or logged only at DEBUG or TRACE levels that are disabled in production environments. The failure to implement these controls in ZKConfig created this information exposure vulnerability.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no privileges, user interaction, or complex conditions to exploit. An attacker can leverage this vulnerability through the following scenarios:

1. Log Aggregation Access: Organizations using centralized logging solutions (ELK Stack, Splunk, CloudWatch) may inadvertently expose ZooKeeper client configuration to users with log viewer access.

2. Backup Compromise: Attackers who compromise backup systems containing log files can extract sensitive configuration data.

3. Shared Hosting Environments: In multi-tenant environments, improper log isolation could allow cross-tenant information leakage.

4. Supply Chain Attacks: Compromised log processing pipelines or third-party log management services could harvest credentials from exposed logs.

The vulnerability does not require active exploitation of the ZooKeeper service itself—rather, it creates a passive information disclosure channel through normal logging operations.

Detection Methods for CVE-2026-24308

Indicators of Compromise

• Review ZooKeeper client log files for exposed configuration values appearing at INFO level
• Check for unusual access patterns to log files or log aggregation systems
• Monitor for unauthorized access to backup systems containing client logs
• Audit log retention systems for potential exposure of sensitive ZooKeeper configuration data

Detection Strategies

• Implement log scanning rules to detect sensitive patterns (credentials, connection strings, API keys) in ZooKeeper client logs
• Deploy file integrity monitoring on log directories to detect unauthorized access
• Configure SIEM rules to alert on bulk log file access or export operations
• Use data loss prevention (DLP) tools to identify credential exposure in log storage

Monitoring Recommendations

• Enable audit logging for access to ZooKeeper client log files and directories
• Monitor log aggregation systems for queries targeting ZooKeeper configuration patterns
• Implement alerting for new service accounts or users accessing log repositories
• Track and baseline normal log access patterns to identify anomalous behavior

How to Mitigate CVE-2026-24308

Immediate Actions Required

• Upgrade Apache ZooKeeper to version 3.8.6 or 3.9.5 which contain the fix for this vulnerability
• Review existing ZooKeeper client logs for exposed sensitive configuration values
• Rotate any credentials or secrets that may have been logged prior to patching
• Restrict access to log files and log aggregation systems to authorized personnel only

Patch Information

Apache has released patched versions that address the improper configuration value logging in ZKConfig. Users running Apache ZooKeeper 3.8.5 should upgrade to version 3.8.6, while users on version 3.9.4 should upgrade to version 3.9.5. The patches implement proper handling of configuration values to prevent sensitive information from being written to client logfiles at INFO level.

For detailed information about the security fix, refer to the Apache Security Announcement and the OpenWall OSS-Security Discussion.

Workarounds

• Temporarily increase logging level above INFO (e.g., WARN or ERROR) to prevent configuration values from being logged
• Implement log filtering at the aggregation layer to redact sensitive configuration patterns
• Restrict file system permissions on ZooKeeper client log directories to minimize exposure risk
• Consider implementing log encryption at rest to protect any previously logged sensitive data

# Configuration example - Temporarily increase logging level to prevent INFO-level exposure
# In log4j.properties or log4j2.xml, set ZooKeeper client logging to WARN level
# log4j.properties example:
log4j.logger.org.apache.zookeeper=WARN

# Alternatively, restrict log file permissions
chmod 600 /var/log/zookeeper/client.log
chown zookeeper:zookeeper /var/log/zookeeper/client.log