CVE-2026-102407: Elasticsearch Auth Bypass Vulnerability

CVE-2026-102407 Overview

CVE-2026-102407 is an Incorrect Authorization vulnerability [CWE-863] affecting Elasticsearch. An authenticated user holding sufficient privileges over a single resource can abuse the Modify Data Streams API to alter a data stream they are not otherwise authorized to modify. Successful exploitation allows attackers to inject data into unauthorized streams or disrupt their searchability. The flaw does not expose stream contents to unauthorized readers, limiting the impact to integrity and availability. Elastic addressed the issue in Elasticsearch versions 8.19.19, 9.3.8, and 9.4.4 as part of security advisory ESA-2026-188.

Critical Impact
Authenticated low-privilege users can modify or corrupt Elasticsearch data streams outside their authorization scope, undermining data integrity and search reliability.

Affected Products

Elasticsearch versions prior to 8.19.19
Elasticsearch 9.x versions prior to 9.3.8
Elasticsearch 9.4 versions prior to 9.4.4

Discovery Timeline

2026-10-06 - CVE-2026-102407 published to NVD
2026-10-07 - Last updated in NVD database

Technical Details for CVE-2026-102407

Vulnerability Analysis

The vulnerability resides in Elasticsearch's Modify Data Streams API authorization logic. The API fails to correctly evaluate whether the requesting principal holds the required privileges across every data stream referenced in the request. An attacker authenticated to the cluster with legitimate privileges over at least one resource can submit modification requests that affect additional data streams outside their intended scope.

The weakness maps to Accessing Functionality Not Properly Constrained by ACLs (CAPEC-1). The flaw affects integrity and availability but does not expose confidential stream contents, since the API does not return the underlying documents in response to modification calls.

Root Cause

The root cause is incorrect authorization enforcement [CWE-863] within the Modify Data Streams API handler. Access-control checks validate privileges on one targeted resource rather than enforcing privilege verification on each data stream the operation would alter. This mismatch between authorization scope and operational scope enables cross-stream modification by a legitimately authenticated user.

Attack Vector

Exploitation requires network access to the Elasticsearch REST API and valid credentials with privileges over at least one data stream. The attacker issues a crafted Modify Data Streams API request referencing target streams they do not own. The server applies the modification without rejecting the request on authorization grounds. No user interaction is required, and the attack can be executed remotely against any reachable Elasticsearch node. See the Elastic Discuss Security Update for vendor technical details.

Detection Methods for CVE-2026-102407

Indicators of Compromise

Unexpected POST or PUT requests to the _data_stream/_modify endpoint from accounts without historical administrative activity.
Audit log entries showing data stream backing index changes initiated by low-privilege users.
Unexplained document counts, mapping drift, or search anomalies in previously stable data streams.

Detection Strategies

Enable Elasticsearch audit logging and alert on invocations of the Modify Data Streams API by non-administrative principals.
Correlate API request logs with role assignments to flag calls that target data streams outside the caller's documented authorization scope.
Baseline normal Modify Data Streams API usage patterns and generate alerts on deviations in frequency, caller identity, or targeted streams.

Monitoring Recommendations

Forward Elasticsearch audit and REST request logs to a centralized analytics platform for retrospective hunting.
Monitor cluster state changes affecting data stream membership and backing index composition.
Track role mapping and privilege changes to detect privilege expansion that could broaden exploitation scope.

How to Mitigate CVE-2026-102407

Immediate Actions Required

Upgrade affected clusters to Elasticsearch 8.19.19, 9.3.8, or 9.4.4 without delay.
Audit existing role definitions and remove unnecessary data stream privileges from non-administrative users.
Review recent Modify Data Streams API activity for signs of unauthorized modification.

Patch Information

Elastic released fixes in Elasticsearch 8.19.19, 9.3.8, and 9.4.4 under advisory ESA-2026-188. Operators running earlier releases on the 8.19.x, 9.3.x, or 9.4.x branches should upgrade to the corresponding patched version. Full release details are available in the Elastic Discuss Security Update.

Workarounds

Restrict access to the Modify Data Streams API by scoping roles tightly to specific data streams rather than broad patterns.
Place Elasticsearch behind an authenticating reverse proxy that enforces path-level restrictions on _data_stream/_modify requests.
Segment administrative and application service accounts so that application-tier credentials cannot invoke data stream modification APIs.

bash

# Configuration example: upgrade Elasticsearch package to a patched release
# Debian/Ubuntu
sudo apt-get update
sudo apt-get install --only-upgrade elasticsearch=8.19.19

# Verify installed version
curl -s -u elastic:$ES_PASSWORD https://localhost:9200/ | grep number