CVE-2023-20891: VMware Isolation Segment Info Disclosure

CVE-2023-20891 Overview

CVE-2023-20891 is an information disclosure vulnerability affecting VMware Tanzu Application Service for VMs and Isolation Segment. The vulnerability stems from improper handling of sensitive credentials, which are logged in hex encoding within platform system audit logs. A malicious non-admin user who gains access to these audit logs can retrieve hex-encoded Cloud Foundry (CF) API admin credentials, potentially enabling them to push malicious versions of applications to the platform.

Critical Impact

Attackers with access to platform audit logs can extract CF API admin credentials and deploy malicious application versions, compromising the integrity of the entire application service environment.

Affected Products

• VMware Tanzu Application Service for Virtual Machines
• VMware Isolation Segment
• Cloud Foundry environments utilizing affected VMware components

Discovery Timeline

• 2023-07-26 - CVE-2023-20891 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-20891

Vulnerability Analysis

This vulnerability falls under CWE-532 (Insertion of Sensitive Information into Log File), a common weakness where applications inadvertently expose sensitive data through logging mechanisms. In this case, VMware Tanzu Application Service and Isolation Segment write CF API admin credentials to platform system audit logs using hex encoding.

While hex encoding provides basic obfuscation, it offers no cryptographic protection and can be trivially reversed to reveal the original credential values. The vulnerability requires network access and low-level privileges to exploit, as the attacker must have some form of authenticated access to the platform to reach the audit logs. In default deployments, non-admin users do not have access to these system audit logs, which provides some mitigation. However, misconfigurations or overly permissive access controls could expose these logs to unauthorized users.

Root Cause

The root cause of CVE-2023-20891 is the improper logging of sensitive authentication credentials within platform system audit logs. The development practice of logging credentials, even in an encoded format, violates secure coding principles that mandate sensitive data should never be written to log files. Hex encoding provides no security benefit as it is a reversible transformation, not encryption. The credentials should have been either excluded from logging entirely or masked with non-recoverable patterns.

Attack Vector

The attack vector is network-based and requires an authenticated user with low privileges. An attacker who has gained access to the platform system audit logs can extract the hex-encoded CF API admin credentials through the following exploitation flow:

1. The attacker obtains authenticated access to the VMware Tanzu Application Service environment
2. Through misconfiguration, privilege escalation, or insider access, they gain read access to platform system audit logs
3. The attacker searches log files for hex-encoded credential patterns
4. The hex-encoded strings are decoded to reveal plaintext CF API admin credentials
5. Using the extracted admin credentials, the attacker can authenticate to the CF API with elevated privileges
6. The attacker pushes malicious application versions or performs other administrative actions

Detection Methods for CVE-2023-20891

Indicators of Compromise

• Unusual access patterns to platform system audit log files or directories
• Unexpected read operations on audit logs by non-administrative accounts
• Authentication attempts using CF API admin credentials from unusual source IPs or at unusual times
• Suspicious application deployments or updates to existing applications
• Log access from accounts that historically have not accessed these resources

Detection Strategies

• Implement file integrity monitoring on platform system audit log directories to detect unauthorized access
• Enable detailed audit logging for all access to log files and correlate with user identity
• Monitor CF API authentication events for anomalous admin credential usage patterns
• Deploy behavioral analytics to identify users accessing resources outside their normal operational scope
• Configure alerts for any application push operations that deviate from established CI/CD pipelines

Monitoring Recommendations

• Establish baselines for normal audit log access patterns and alert on deviations
• Implement real-time monitoring of CF API admin authentication events with geographic and temporal correlation
• Deploy SentinelOne agents across the Tanzu Application Service infrastructure for comprehensive visibility
• Configure centralized log aggregation with access controls to detect credential harvesting attempts
• Review and audit platform access permissions on a regular schedule to identify overly permissive configurations

How to Mitigate CVE-2023-20891

Immediate Actions Required

• Apply the security patches provided by VMware as documented in VMware Security Advisory VMSA-2023-0016
• Rotate all CF API admin credentials immediately, even if no compromise is suspected
• Audit and restrict access to platform system audit logs to only essential personnel
• Review existing audit logs for evidence of unauthorized access or credential extraction
• Implement network segmentation to limit access to log storage systems

Patch Information

VMware has released security updates to address this vulnerability. Organizations should consult VMware Security Advisory VMSA-2023-0016 for specific patch versions and upgrade instructions. The patches address the credential logging issue by preventing sensitive credentials from being written to audit logs in any format. Organizations should prioritize applying these patches and plan for credential rotation as part of the remediation process.

Workarounds

• Restrict access to platform system audit logs using role-based access controls, ensuring only authorized administrators can read these files
• Implement log sanitization processes to remove or mask sensitive data from historical logs
• Deploy additional access controls and monitoring around log storage systems
• Consider relocating audit logs to isolated storage with stricter access policies until patches can be applied
• Enable multi-factor authentication for all administrative access to reduce the impact of credential exposure

# Example: Rotate CF API admin credentials after patching
cf set-org-role new-admin-user org-name OrgManager
cf set-space-role new-admin-user org-name space-name SpaceManager
# Review and revoke access for potentially compromised credentials
cf unset-org-role compromised-user org-name OrgManager