CVE-2023-38037: ActiveSupport Information Disclosure Flaw

CVE-2023-38037 Overview

CVE-2023-38037 is an insecure file permissions vulnerability affecting the ActiveSupport::EncryptedFile component in Ruby on Rails. When users edit encrypted files, the application writes contents that will be encrypted to a temporary file. This temporary file's permissions default to the user's current umask settings, which may allow other users on the same system to read the sensitive contents before encryption occurs.

Attackers with local file system access could exploit this race condition window to read the plaintext contents of encrypted files while a user is actively editing them. This represents a significant confidentiality risk, particularly in multi-user environments or shared hosting scenarios.

Critical Impact

Sensitive data stored in Rails encrypted credentials files could be exposed to unauthorized local users during editing operations, potentially revealing API keys, database passwords, and other secrets.

Affected Products

• Ruby on Rails applications using ActiveSupport::EncryptedFile
• Rails applications utilizing encrypted credentials (rails credentials:edit)
• NetApp products using affected Ruby on Rails versions (see NetApp Security Advisory)

Discovery Timeline

• 2025-01-09 - CVE CVE-2023-38037 published to NVD
• 2025-02-15 - Last updated in NVD database

Technical Details for CVE-2023-38037

Vulnerability Analysis

This vulnerability falls under CWE-732 (Incorrect Permission Assignment for Critical Resource). The core issue lies in how ActiveSupport::EncryptedFile handles temporary file creation during the encryption workflow.

When a user invokes the encrypted file editing functionality (commonly through rails credentials:edit), the system decrypts the encrypted file contents and writes them to a temporary file so the user can edit them in their preferred text editor. The problem is that this temporary file inherits permissions based on the system's umask rather than being explicitly restricted to the current user.

In typical Unix/Linux environments, the default umask of 022 would result in world-readable temporary files (permissions 644), allowing any local user to read the decrypted contents. Even with a more restrictive umask of 027, group members could still access the file.

Root Cause

The root cause is the absence of explicit file permission settings when creating the temporary file in ActiveSupport::EncryptedFile. The code relies on the system's default umask configuration rather than explicitly setting restrictive permissions (such as 0600) on temporary files containing sensitive decrypted data.

This is a common security oversight in applications handling sensitive temporary data, where developers assume the system umask will provide adequate protection, but fail to account for varied deployment environments and multi-user systems.

Attack Vector

The attack requires local access to the file system and exploits a time-of-check-time-of-use (TOCTOU) race condition window. The attack sequence involves:

1. An attacker with local system access monitors the /tmp directory or known Rails temporary file locations
2. When a legitimate user begins editing encrypted credentials, the decrypted content is written to a temporary file
3. Due to permissive file permissions, the attacker reads the temporary file contents during the editing window
4. The attacker obtains plaintext secrets including API keys, database credentials, and other sensitive configuration data

This attack is most effective in shared hosting environments, multi-tenant systems, or any scenario where multiple users have shell access to the same server running Rails applications.

Detection Methods for CVE-2023-38037

Indicators of Compromise

• Unusual file access patterns in temporary directories by non-application users
• Unexpected read operations on Rails temporary files from unauthorized user accounts
• File system audit logs showing access to /tmp files matching Rails encrypted file patterns
• Evidence of local user enumeration or privilege reconnaissance activities

Detection Strategies

• Enable file system auditing (auditd on Linux) for temporary directories used by Rails applications
• Monitor for suspicious file reads from users other than the Rails application owner
• Implement host-based intrusion detection to flag access patterns indicative of local information harvesting
• Review Rails application logs for encrypted credential editing events and correlate with file system access logs

Monitoring Recommendations

• Configure file integrity monitoring for directories where Rails writes temporary encrypted file contents
• Set up alerts for any non-owner read access to Rails application temporary files
• Monitor system authentication logs for new or unusual local user sessions during Rails credential editing operations
• Implement centralized logging to correlate file access events across multi-user systems

How to Mitigate CVE-2023-38037

Immediate Actions Required

• Upgrade Ruby on Rails to a patched version that addresses this vulnerability
• Review and restrict system umask settings to more secure defaults (e.g., 077)
• Limit local system access to trusted administrators only
• Audit existing Rails encrypted credentials for potential exposure and rotate any secrets that may have been compromised

Patch Information

Ruby on Rails has released patched versions addressing this vulnerability. Organizations should upgrade to the latest Rails version that includes the fix for CVE-2023-38037. For detailed patch information and affected versions, consult the Ruby on Rails CVE Discussion.

NetApp has also published guidance for their affected products in their security advisory.

Workarounds

• Set a restrictive system-wide umask of 077 before running rails credentials:edit
• Perform encrypted credential editing only on dedicated, single-user systems
• Use containers or isolated environments when editing Rails encrypted files to prevent local user access
• Implement mandatory access controls (SELinux, AppArmor) to restrict temporary file access to the application user

# Configuration example
# Set restrictive umask before editing Rails credentials
umask 077
rails credentials:edit

# Or create a wrapper script for credential editing
#!/bin/bash
# secure-credentials-edit.sh
OLD_UMASK=$(umask)
umask 077
rails credentials:edit
umask $OLD_UMASK