CVE-2025-12148 is a vulnerability affecting floragunn Search Guard FLX, a security plugin for Elasticsearch, specifically versions 3.1.1 and earlier. The issue lies in the improper enforcement of Field Masking (FM) rules on fields of type IP address. While the plugin correctly redacts IP address fields in the _source document returned by search queries, it fails to prevent information leakage through search hits. An attacker can perform targeted searches using specific IP values and observe which documents are returned, effectively reconstructing the original IP addresses despite the masking. This side-channel exposure violates confidentiality by leaking sensitive IP information to unauthorized actors. The vulnerability requires the attacker to have low-level privileges (authenticated with limited rights) but does not require user interaction. The CVSS 4.0 score is 6.0 (medium severity), reflecting network attack vector, low attack complexity, partial authentication, and high confidentiality impact. No known public exploits exist yet. The vendor recommends upgrading to a fixed version; if immediate upgrade is not possible, applying field level security (FLS) on IP fields instead of field masking can mitigate the issue. This vulnerability is categorized under CWE-200 (Exposure of Sensitive Information) and CWE-732 (Incorrect Permission Assignment for Critical Resource).

For European organizations, this vulnerability poses a risk of unauthorized disclosure of sensitive IP address information stored in Elasticsearch clusters protected by Search Guard FLX. Such IP data could relate to internal network infrastructure, client addresses, or other critical assets. Exposure could facilitate reconnaissance by threat actors, enabling targeted attacks or lateral movement within networks. Sectors such as finance, telecommunications, energy, and government agencies that rely heavily on Elasticsearch for log aggregation and security analytics are particularly at risk. The breach of confidentiality could lead to regulatory non-compliance under GDPR, resulting in legal and financial penalties. Although the vulnerability does not enable direct data modification or denial of service, the leakage of sensitive network information can undermine overall security posture and trust. The requirement for authentication limits exposure to insiders or compromised accounts, but the low privilege needed means many users could potentially exploit this flaw.

1. Upgrade Search Guard FLX to the latest version that addresses CVE-2025-12148 as soon as it becomes available from floragunn. 2. Until an upgrade is possible, implement field level security (FLS) on IP address fields instead of relying on field masking to prevent unauthorized access to sensitive IP data. 3. Review and tighten user privileges to minimize the number of accounts with access to search functionality, especially those with permissions to query IP fields. 4. Monitor Elasticsearch query logs for unusual or targeted searches involving IP address fields that could indicate exploitation attempts. 5. Conduct internal audits of data classification and ensure sensitive IP information is only stored and accessible where strictly necessary. 6. Educate security and IT teams about this vulnerability and the importance of applying the recommended mitigations promptly. 7. Consider network segmentation and additional access controls around Elasticsearch clusters to reduce the risk of insider threats exploiting this vulnerability.