CVE-2026-20240: Splunk Enterprise DoS Vulnerability

CVE-2026-20240 Overview

CVE-2026-20240 is a Denial of Service vulnerability in Splunk Enterprise and Splunk Cloud Platform. The flaw resides in the coldToFrozen.sh script bundled with the splunk_archiver app. A low-privileged authenticated user who does not hold the admin or power Splunk roles can invoke the script with arbitrary file paths. The script renames the target directories without validating input or restricting operations to safe locations. An attacker can rename critical Splunk directories, rendering the instance non-functional. The vulnerability is tracked under [CWE-20] Improper Input Validation.

Critical Impact

A low-privileged authenticated user can rename critical Splunk directories through coldToFrozen.sh, causing a Denial of Service that makes the Splunk instance non-functional.

Affected Products

• Splunk Enterprise versions below 10.2.2, 10.0.5, 9.4.11, and 9.3.12
• Splunk Cloud Platform versions below 10.4.2603.1, 10.3.2512.9, 10.2.2510.11, 10.1.2507.21, 10.0.2503.13, and 9.3.2411.129
• splunk_archiver app shipped with the affected Splunk releases

Discovery Timeline

• 2026-05-20 - CVE-2026-20240 published to NVD
• 2026-05-20 - Last updated in NVD database

Technical Details for CVE-2026-20240

Vulnerability Analysis

The vulnerability exists in the coldToFrozen.sh shell script distributed with the splunk_archiver application. The script is designed to handle the transition of cold Splunk index buckets to frozen storage. It accepts file path arguments and performs rename operations on those paths. The script does not validate or sanitize the supplied paths and does not restrict operations to directories owned by the archiver workflow. A user authenticated with a low-privileged Splunk role can invoke the script and target arbitrary directories. Renaming directories that Splunk depends on at runtime, such as index storage, configuration, or binary paths, causes the instance to stop functioning. Recovery requires manual intervention by an administrator to restore the renamed directories.

Root Cause

The root cause is missing input validation in coldToFrozen.sh. The script accepts arbitrary file paths from the caller and performs filesystem rename operations without enforcing an allowlist of safe directories. There is also no privilege check that limits invocation to the admin or power Splunk roles, so any authenticated low-privileged user can trigger the operation.

Attack Vector

The attack vector is network-based and requires low privileges with no user interaction. An authenticated attacker without admin or power roles invokes the coldToFrozen.sh script through the Splunk interface and supplies a path that points to a directory critical for Splunk operation. The script renames the directory, and the Splunk instance becomes non-functional. Confidentiality and integrity are not directly impacted; availability is the affected dimension.

No verified public proof-of-concept code is available. See the Splunk Security Advisory SVD-2026-0504 for vendor-supplied technical details.

Detection Methods for CVE-2026-20240

Indicators of Compromise

• Execution of coldToFrozen.sh from the splunk_archiver app by accounts that do not hold the admin or power Splunk role.
• Unexpected directory rename operations on Splunk-owned paths such as $SPLUNK_HOME, index directories, or etc/system/local.
• Splunk service failures, missing index buckets, or startup errors referencing absent directories shortly after archiver script invocation.

Detection Strategies

• Audit Splunk internal logs in _audit and _internal indexes for invocations of coldToFrozen.sh and correlate the calling user against assigned Splunk roles.
• Monitor process execution telemetry on Splunk hosts for coldToFrozen.sh runs that pass arguments outside expected frozen-archive paths.
• Flag filesystem rename events against $SPLUNK_HOME and its subdirectories using endpoint or host-based file integrity monitoring.

Monitoring Recommendations

• Forward host process auditing data and Splunk audit logs to a centralized analytics platform for cross-source correlation.
• Build an alert that triggers when coldToFrozen.sh is invoked by any user whose role membership does not include admin or power.
• Track Splunk service availability metrics and tie service-down events back to recent script executions for incident scoping.

How to Mitigate CVE-2026-20240

Immediate Actions Required

• Upgrade Splunk Enterprise to version 10.2.2, 10.0.5, 9.4.11, 9.3.12, or later as appropriate for your branch.
• Confirm Splunk Cloud Platform instances are running 10.4.2603.1, 10.3.2512.9, 10.2.2510.11, 10.1.2507.21, 10.0.2503.13, 9.3.2411.129, or later.
• Review accounts that lack admin or power roles and validate they should retain access to the Splunk instance.

Patch Information

Splunk has released fixed versions that address the missing input validation in coldToFrozen.sh. Refer to the Splunk Security Advisory SVD-2026-0504 for the full list of patched versions and upgrade instructions. Splunk Cloud Platform instances receive the fix through scheduled platform maintenance.

Workarounds

• Restrict execution permissions on coldToFrozen.sh within the splunk_archiver app so that only administrative service accounts can run it.
• Disable or remove the splunk_archiver app on instances that do not require cold-to-frozen archival functionality.
• Audit Splunk role assignments and remove unnecessary low-privileged accounts until the patch is applied.

# Verify Splunk Enterprise version and review archiver script permissions
$SPLUNK_HOME/bin/splunk version
ls -l $SPLUNK_HOME/etc/apps/splunk_archiver/bin/coldToFrozen.sh
# Restrict execution to the splunk service owner only
chmod 700 $SPLUNK_HOME/etc/apps/splunk_archiver/bin/coldToFrozen.sh