CVE-2026-56148: Elasticsearch Uncontrolled Recursion Denial of Service

Technical summary

Elasticsearch contains an uncontrolled recursion flaw (CWE-674) in its query execution engine. When a specially crafted query is submitted, the parser or query optimizer enters a recursive loop without proper depth or resource limits, leading to exhaustion of heap memory and CPU cycles. This manifests as Excessive Allocation (CAPEC-130), rendering the targeted node unable to serve legitimate requests. The vulnerability does not compromise confidentiality or integrity of data; impact is limited to availability. The attack vector is network-accessible, requires low complexity, and necessitates prior authentication—reflected in the CVSS 3.1 score of 6.5 (MEDIUM).

Business impact

For organizations running Elasticsearch as a core search or analytics platform, this vulnerability poses a service disruption risk. A malicious insider or compromised application account could selectively disable cluster nodes, fragmenting the cluster and degrading search latency, analytics pipelines, or security monitoring tools that depend on Elasticsearch. Recovery requires manual node restart. Depending on cluster architecture and data replication, a single-node outage may degrade performance; a multi-node attack could trigger failover cascades. Organizations relying on Elasticsearch for security event ingestion or threat detection should prioritize remediation to prevent adversaries from obscuring their activity by disabling logging infrastructure.

Affected systems

The vulnerability affects Elasticsearch. Specific version ranges are not enumerated in the vulnerability record; consult the Elastic security advisory or check your vendor advisory for exact affected versions and patched releases. Any Elasticsearch deployment with users or applications granted query privileges is potentially at risk.

Exploitability

Exploitation requires network access and valid credentials. The attack is straightforward: submit a malicious query string. The CVSS vector (AV:N/AC:L) indicates no special attack complexity; once authenticated, the attacker need not interact with other users or bypass additional controls. However, the requirement for prior authentication (PR:L) significantly raises the bar compared to unauthenticated denial-of-service attacks. The threat is primarily from insiders, compromised API keys, or lateral movement by an attacker who has obtained Elasticsearch credentials. As of the current data, this vulnerability is not tracked in the CISA KEV catalog, suggesting either limited in-the-wild exploitation or recent disclosure.

Remediation

Apply the patch released by Elastic for CVE-2026-56148 to affected Elasticsearch versions. Verify the exact patched version from the vendor advisory. In parallel, implement access controls to restrict query privileges to trusted applications and users; disable or revoke credentials for unused accounts. Consider network-level segmentation to limit which hosts can reach Elasticsearch query endpoints. Monitor for suspicious query patterns or repeated node crashes that may indicate exploitation attempts.

Patch guidance

Contact Elastic or consult their official security advisory for patched version numbers and update procedures. Elasticsearch typically supports rolling cluster upgrades with minimal downtime. Test patches in a staging environment first, especially if running multi-node clusters or in high-availability setups. Coordinate patching across cluster nodes to avoid cascading failures. If immediate patching is not feasible, restrict query access via firewall rules or role-based access control (RBAC) to reduce the attack surface.

Detection guidance

Monitor Elasticsearch logs for sudden increases in query processing time, memory spikes, or node crashes following authentication events. Look for GC (garbage collection) logs showing full heap exhaustion. Implement queries that flag deep recursion or unusually complex query structures submitted by authenticated users. Network-based detection is limited since the attack payload is a valid query; focus on behavioral anomalies at the application layer. Set alerts for node unavailability or repeated restarts. If available, enable query audit logging to capture the malicious query structure for post-incident analysis.

Why prioritize this

While the CVSS score is MEDIUM (6.5), prioritization depends on your Elasticsearch deployment's role. If Elasticsearch is integral to security monitoring, incident response, or business-critical analytics, treat this as HIGH priority to prevent adversaries from disabling visibility. If it is primarily used for non-security log aggregation or internal search, prioritization can follow standard MEDIUM guidance. The requirement for authentication limits exposure but does not eliminate risk in environments with multiple applications, service accounts, or where credentials are shared or easily compromised.

Risk score, explained

The CVSS 3.1 base score of 6.5 reflects a MEDIUM severity: network-accessible (AV:N), low attack complexity (AC:L), but requiring authentication (PR:L). The attack has a complete impact on availability (A:H) but no impact on confidentiality or integrity (C:N/I:N). The score does not account for environmental factors such as the critical role Elasticsearch may play in your threat detection pipeline or the likelihood of insider threats in your organization; adjust priority based on your risk tolerance and Elasticsearch's criticality.

Frequently asked questions