CVE-2023-5256: Drupal Privilege Escalation Vulnerability

CVE-2023-5256 Overview

CVE-2023-5256 is an information disclosure vulnerability affecting Drupal's JSON:API module that can lead to privilege escalation. In certain scenarios, the JSON:API module outputs error backtraces that may expose sensitive information. When specific caching configurations are in place, this sensitive data can be cached and subsequently made available to anonymous users, potentially enabling unauthorized privilege escalation.

Critical Impact

Sensitive information cached and exposed to anonymous users can lead to privilege escalation, compromising site confidentiality and integrity.

Affected Products

• Drupal Core with JSON:API module enabled
• Drupal versions with vulnerable JSON:API implementations
• Sites utilizing caching configurations that store error responses

Discovery Timeline

• 2023-09-28 - CVE-2023-5256 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-5256

Vulnerability Analysis

This vulnerability stems from improper handling of error responses in Drupal's JSON:API module. When certain error conditions occur, the module generates detailed backtraces that may contain sensitive configuration data, internal paths, database credentials, or other security-critical information. The vulnerability is classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor).

The attack requires network access and some level of authenticated access to trigger the error conditions. However, the critical aspect is that once sensitive information is leaked into error responses, caching mechanisms may store this data and serve it to unauthenticated users, effectively escalating their privileges by exposing information they should not have access to.

Importantly, only sites with the JSON:API module enabled are affected. The core REST module and contributed GraphQL modules are not impacted by this vulnerability.

Root Cause

The root cause lies in the JSON:API module's error handling implementation, which fails to properly sanitize or suppress detailed backtrace information in error responses under certain conditions. When combined with caching layers that do not differentiate between authenticated and unauthenticated request contexts for error responses, sensitive data becomes persistently exposed.

Attack Vector

The attack vector is network-based, requiring an attacker to trigger specific error conditions in the JSON:API module. The exploitation scenario involves:

1. An attacker with low-level privileges sends crafted requests to JSON:API endpoints designed to trigger error conditions
2. The JSON:API module returns detailed backtrace information in error responses
3. Caching mechanisms store these error responses without proper access control segregation
4. Anonymous users subsequently access cached error responses containing sensitive information
5. Exposed information can be leveraged for further attacks or privilege escalation

The vulnerability mechanism involves improper error handling in the JSON:API module's response generation. When errors occur during API request processing, the module may include stack traces and internal application state in the response body. For detailed technical information, refer to the Drupal Security Advisory SA-CORE-2023-006.

Detection Methods for CVE-2023-5256

Indicators of Compromise

• Unexpected backtrace data appearing in JSON:API response logs
• Cached responses containing internal path information or configuration details
• Anomalous access patterns to JSON:API endpoints from anonymous users
• Error responses in cache storage that contain sensitive application data

Detection Strategies

• Monitor JSON:API endpoint responses for unexpected backtrace or debug information
• Audit cache contents for sensitive information exposure
• Review web server logs for unusual error response patterns on API endpoints
• Implement content inspection rules to detect backtrace patterns in outbound API responses

Monitoring Recommendations

• Enable detailed logging for JSON:API module activity
• Configure cache monitoring to alert on storage of error responses
• Set up intrusion detection signatures for error backtrace patterns in HTTP responses
• Monitor for privilege escalation indicators following API error events

How to Mitigate CVE-2023-5256

Immediate Actions Required

• Apply the latest Drupal security update as referenced in SA-CORE-2023-006
• If immediate patching is not possible, disable the JSON:API module
• Clear all caches after applying patches or mitigations
• Review cached content for any previously exposed sensitive information

Patch Information

Drupal has released security patches to address this vulnerability. Administrators should update to the latest patched version of Drupal Core as detailed in the Drupal Security Advisory SA-CORE-2023-006. After applying the update, ensure all site caches are cleared to remove any potentially compromised cached data.

Workarounds

• Uninstall or disable the JSON:API module if it is not required for site functionality
• Configure caching layers to exclude error responses from being cached
• Implement response filtering to strip backtrace information from API outputs
• Restrict access to JSON:API endpoints using web server or firewall rules

# Disable JSON:API module via Drush (temporary workaround)
drush pm:uninstall jsonapi

# Clear all Drupal caches after applying mitigation
drush cache:rebuild