CVE-2025-13653: Search Guard FLX Auth Bypass Flaw

CVE-2025-13653 Overview

CVE-2025-13653 is a medium-severity information disclosure vulnerability affecting Search Guard FLX, a security plugin for Elasticsearch. In Search Guard FLX versions from 3.1.0 up to 4.0.0 with enterprise modules being disabled, an issue exists which allows authenticated users to use specially crafted requests to read documents from data streams without having the respective privileges.

This vulnerability is classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor), indicating that the core issue stems from improper access control allowing unauthorized data access through crafted requests.

Critical Impact

Authenticated users can bypass privilege restrictions to read sensitive documents from data streams, potentially exposing confidential information stored in Elasticsearch clusters protected by Search Guard FLX.

Affected Products

• Search Guard FLX versions 3.1.0 to 4.0.0 (with enterprise modules disabled)

Discovery Timeline

• 2025-12-01 - CVE-2025-13653 published to NVD
• 2025-12-02 - Last updated in NVD database

Technical Details for CVE-2025-13653

Vulnerability Analysis

This vulnerability carries a CVSS v3.1 base score of 4.3 (Medium severity) with the vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N.

The EPSS (Exploit Prediction Scoring System) data indicates:

• EPSS Score: 0.026%
• EPSS Percentile: 6.598

This relatively low EPSS score suggests limited probability of exploitation in the wild, though the vulnerability remains a concern for environments running affected versions.

Root Cause

The vulnerability stems from an authorization bypass issue in Search Guard FLX's access control mechanism when enterprise modules are disabled. The security plugin fails to properly validate user privileges when processing requests targeting data streams, allowing authenticated users to circumvent intended access restrictions.

When enterprise modules are disabled, the reduced security controls create a gap in privilege enforcement specifically for data stream access. This represents a broken access control condition where the application does not adequately verify that a user has the necessary permissions before granting access to sensitive data stream documents.

Attack Vector

The attack vector is network-based, requiring low attack complexity. An authenticated attacker can exploit this vulnerability by crafting specialized requests targeting data streams within the Elasticsearch cluster. The attack does not require user interaction and can be performed remotely over the network.

The exploitation path involves:

1. An attacker authenticates to the Elasticsearch cluster using valid (potentially low-privileged) credentials
2. The attacker identifies data streams containing sensitive information they should not have access to
3. The attacker crafts specialized requests designed to bypass privilege checks
4. Due to the vulnerability in Search Guard FLX's access control, the requests succeed despite insufficient privileges
5. The attacker receives document contents from the targeted data streams

Since no verified exploit code is available, the specific request structure required to exploit this vulnerability is not publicly documented. Security teams should refer to the Search Guard advisory for technical details.

Detection Methods for CVE-2025-13653

Indicators of Compromise

• Unusual data stream access patterns from users who should not have privileges to specific data streams
• Audit logs showing successful reads of data stream documents by users lacking explicit read permissions
• Anomalous query patterns targeting multiple data streams across the cluster

Detection Strategies

Organizations can implement the following detection strategies:

1. Audit Log Analysis: Enable comprehensive audit logging in Search Guard FLX and monitor for data stream access by users who lack explicit privileges to those streams.

2. Access Pattern Monitoring: Establish baseline access patterns for users and alert on deviations, particularly when users access data streams outside their normal scope.

3. Version Verification: Verify the Search Guard FLX version in use. Systems running versions 3.1.0 through 4.0.0 with enterprise modules disabled are potentially vulnerable.

4. Configuration Review: Check whether enterprise modules are enabled or disabled, as the vulnerability specifically affects configurations with enterprise modules disabled.

Monitoring Recommendations

• Implement real-time monitoring of Elasticsearch audit logs for unauthorized data stream access attempts
• Configure alerts for any successful data stream document retrievals by users without explicit permissions
• Deploy network traffic analysis to identify anomalous patterns of Elasticsearch queries
• Establish regular reviews of user privilege assignments versus actual access patterns

How to Mitigate CVE-2025-13653

Immediate Actions Required

• Upgrade Search Guard FLX to version 4.0.1 or later immediately
• Enable enterprise modules if possible, as the vulnerability specifically affects configurations with enterprise modules disabled
• Review and restrict user authentication to minimize the pool of potential attackers
• Audit data stream access logs to identify any potential past exploitation

Patch Information

Search Guard has released version 4.0.1 which addresses this vulnerability. The fix is documented in the Search Guard FLX 4.0.1 Changelog.

Organizations should prioritize upgrading to the patched version. Additional information about this CVE and related security advisories can be found at the Search Guard CVE Advisory page.

Workarounds

If immediate patching is not possible, organizations should consider the following temporary mitigations:

1. Enable Enterprise Modules: If licensing permits, enabling enterprise modules may provide additional security controls that mitigate this vulnerability.

2. Restrict Authentication: Limit authenticated access to only essential users and services, reducing the potential attack surface.

3. Network Segmentation: Isolate Elasticsearch clusters to reduce network-based attack vectors.

4. Enhanced Monitoring: Implement strict monitoring of data stream access patterns until the patch can be applied.

# Verify current Search Guard FLX version
curl -XGET "https://localhost:9200/_searchguard/health" -k

# Check if enterprise modules are enabled
curl -XGET "https://localhost:9200/_searchguard/license" -k

# Review audit logging configuration to ensure data stream access is logged
# Ensure sgconfig/sg_audit.yml has appropriate settings enabled