Description

A flaw in Elasticsearch allows a low-privileged authenticated user who can index documents to submit a single small document containing a crafted user-supplied input. Processing one such document occupies a worker thread from a bounded pool for a disproportionate amount of time, degrading the availability of indexing operations on the affected node.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "4.3",
  "pubDate": "2026-08-13T20:17:29.217Z",
  "pubdate": "2026-08-13T20:17:29.217Z",
  "executiveSummary": "A denial of service vulnerability exists within Elasticsearch, specifically affecting indexing operations across vulnerable deployments. The flaw enables a low-privileged authenticated user who possesses permissions to index documents to compromise cluster availability. By submitting a single, small document containing crafted user-supplied input, an attacker can force the processing engine to consume excessive computational resources.\nThe vulnerability manifests as a resource exhaustion condition where processing the malicious payload occupies a worker thread from a bounded thread pool for a disproportionate amount of time. This starvation of worker threads degrades the availability of critical indexing operations on the affected node, potentially cascading across the cluster if left unmitigated. The exploitation requirement is minimal, needing only low-privileged authentication and the baseline ability to index documents, making insider threats or compromised low-level accounts significant risk vectors.\nThe primary impact is service degradation and potential denial of service regarding data ingestion capabilities. Because the vulnerability targets bounded worker pools through lightweight inputs, traditional rate-limiting or volumetric mitigations may prove insufficient without specific application-layer input validation or software patches. Organizations running affected Elasticsearch versions face operational availability risks if malicious actors exploit this processing bottleneck.",
  "technicalDetails": "The vulnerability stems from insufficient validation or inefficient handling of crafted user-supplied input during the document indexing pipeline within Elasticsearch. The affected component is responsible for parsing and processing incoming documents within a bounded thread pool dedicated to indexing operations.\nThe root cause lies in algorithmic complexity or blocking behavior when parsing specific input structures. When an authenticated attacker submits a crafted document, the computational complexity required by the processing engine to handle the payload is disproportionately high relative to the physical size of the document itself. This forces the assigned worker thread to spend an anomalous duration executing tasks related to the single document.\nThe attack flow proceeds as follows: First, the adversary authenticates to the Elasticsearch cluster using credentials associated with a low-privileged role that includes document indexing privileges. Second, the attacker constructs a small payload containing the malicious user-supplied input designed to trigger the processing inefficiency. Third, the attacker issues a standard indexing request containing this crafted document to the target node. Fourth, upon receiving the request, Elasticsearch assigns a worker thread from the bounded pool to process the document. Fifth, due to the crafted input, the thread becomes tied up for an extended, disproportionate amount of time, exhausting the available concurrency limit for indexing operations.\nBecause the thread pool is bounded, concurrent legitimate indexing requests are queued or rejected, resulting in degraded availability, increased latency, and a localized denial of service on the affected node. The attack requires low-privileged authentication, active document indexing capabilities, and network access to the Elasticsearch HTTP/REST interface. No post-exploitation privilege escalation is implied by this specific flaw, as the primary impact is strictly focused on resource exhaustion and operational availability degradation."
}