CVE-2026-76340 Overview
CVE-2026-76340 is a missing authorization vulnerability [CWE-862] in Splunk Enterprise 10.4 versions below 10.4.2. The Representational State Transfer (REST) API exposes a token-signing key reload action without requiring authentication or the change_authentication capability. An unauthenticated remote attacker can invoke the endpoint to force Splunk Enterprise to reload token-signing keys. Splunk Enterprise versions below 10.4 are not affected because the affected code path does not exist in earlier releases.
Critical Impact
An unauthenticated network-based attacker can trigger token-signing key reloads on affected Splunk Enterprise deployments, causing integrity impact to the authentication subsystem.
Affected Products
- Splunk Enterprise 10.4.0
- Splunk Enterprise 10.4.1
- Splunk Enterprise versions below 10.4.2 (10.4 branch only)
Discovery Timeline
- 2026-08-19 - CVE-2026-76340 published to the National Vulnerability Database (NVD)
- 2026-08-20 - Last updated in NVD database
Technical Details for CVE-2026-76340
Vulnerability Analysis
The vulnerability resides in a Splunk Enterprise REST API endpoint responsible for reloading token-signing keys. Splunk uses token-signing keys to validate authentication tokens issued to users and services. Reloading these keys is an administrative action that should be gated behind authentication and the change_authentication capability, as documented in the Splunk role capability model.
In affected 10.4 builds prior to 10.4.2, the REST handler for the token-key reload action performs the reload without verifying the caller's identity or capability set. Any network-reachable client that can send an HTTP request to the management port can invoke the operation. The result is an integrity impact on Splunk's authentication material handling, without direct confidentiality or availability consequences per the published CVSS metrics.
Root Cause
The root cause is a missing authorization check [CWE-862] on a privileged REST endpoint. The handler does not enforce the change_authentication capability requirement that applies to related authentication management actions. Because the code path is new to the 10.4 branch, earlier releases do not expose the flaw.
Attack Vector
Exploitation requires network access to the Splunk Enterprise management REST API, typically served on TCP port 8089. The attacker sends an HTTP request to the token-key reload endpoint without credentials. No user interaction is required. Refer to the Splunk Security Advisory SVD-2026-0801 for authoritative endpoint details. No public proof-of-concept exploit is currently available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.
Detection Methods for CVE-2026-76340
Indicators of Compromise
- Unauthenticated HTTP requests to Splunk REST endpoints on the management port (default 8089) that trigger token-key reload actions.
- splunkd_access.log entries showing REST calls to authentication or token-key handlers from unexpected source addresses without associated user context.
- Unexpected token-signing key reload events in Splunk internal audit logs (_audit index).
Detection Strategies
- Search the _internal and _audit indexes for token-key reload events and correlate them with authenticated administrator sessions. Reloads without a corresponding authenticated session indicate exploitation.
- Monitor splunkd_access.log for REST requests to token or authentication reload endpoints returning HTTP 200 without an associated user= field.
- Alert on any REST API access to the Splunk management port from source IPs outside the administrative network segment.
Monitoring Recommendations
- Restrict network exposure of TCP 8089 to trusted management subnets and log all inbound connections.
- Enable and forward Splunk audit logs to an independent monitoring system so that log tampering does not blind detection.
- Baseline the frequency of legitimate token-key reload events and alert on deviations.
How to Mitigate CVE-2026-76340
Immediate Actions Required
- Upgrade Splunk Enterprise 10.4 deployments to version 10.4.2 or later.
- Inventory all Splunk Enterprise instances and confirm which run 10.4.0 or 10.4.1.
- Restrict access to the Splunk management REST port (default 8089) to trusted administrative networks using firewall rules or host-based controls.
- Review Splunk audit logs for prior token-key reload events that do not correspond to authorized administrator activity.
Patch Information
Splunk has addressed the vulnerability in Splunk Enterprise 10.4.2. See the Splunk Security Advisory SVD-2026-0801 for the vendor's official remediation guidance. Deployments on the 9.x or earlier branches are not affected and do not require action for this CVE.
Workarounds
- Block network access to the Splunk management port from untrusted networks using perimeter and host firewalls.
- Place Splunk Enterprise management interfaces behind a VPN or bastion host until patching is complete.
- Follow the guidance in the Splunk documentation on defining roles with capabilities to review and tighten role assignments after upgrading.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
