CVE-2023-32708: Splunk Enterprise Auth Bypass Vulnerability

CVE-2023-32708 Overview

CVE-2023-32708 is an HTTP Response Splitting vulnerability affecting Splunk Enterprise and Splunk Cloud Platform. A low-privileged user can exploit this flaw using the rest SPL command to manipulate HTTP responses, potentially gaining unauthorized access to other REST endpoints within the system. This vulnerability allows attackers with minimal privileges to bypass access controls and interact with sensitive API endpoints that should be restricted.

Critical Impact

Low-privileged users can exploit the rest SPL command to access arbitrary REST endpoints, potentially leading to unauthorized data access, privilege escalation, and compromise of Splunk infrastructure integrity.

Affected Products

• Splunk Enterprise versions below 9.0.5
• Splunk Enterprise versions below 8.2.11
• Splunk Enterprise versions below 8.1.14
• Splunk Cloud Platform versions below 9.0.2303.100

Discovery Timeline

• June 1, 2023 - CVE-2023-32708 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-32708

Vulnerability Analysis

This HTTP Response Splitting vulnerability (CWE-113) exists in the rest SPL command implementation within Splunk Enterprise and Splunk Cloud Platform. The vulnerability stems from improper neutralization of CRLF sequences in HTTP headers, combined with interpretation conflict issues (CWE-436). When a user crafts a malicious SPL query using the rest command, they can inject CRLF characters that split the HTTP response, effectively creating additional HTTP responses or manipulating existing ones.

The attack is particularly concerning because it requires only low-privilege authentication to execute. An attacker with basic user access to Splunk can leverage this vulnerability to forge requests to internal REST endpoints that would normally require elevated permissions, potentially exposing sensitive configuration data, user credentials, or system information.

Root Cause

The root cause lies in insufficient input validation and sanitization of user-controlled data within the rest SPL command. The command fails to properly neutralize CRLF (Carriage Return Line Feed) sequences before including user input in HTTP response headers. This allows attackers to terminate the current HTTP header section prematurely and inject arbitrary headers or response bodies, effectively hijacking the HTTP response mechanism.

Attack Vector

The attack is network-based and requires only low-privilege authentication to the Splunk platform. An attacker with valid user credentials can craft malicious SPL queries containing the rest command with specially crafted parameters. By injecting CRLF sequences (\r\n) into the command parameters, the attacker can manipulate HTTP responses to access restricted REST API endpoints.

The vulnerability does not require user interaction, meaning an authenticated attacker can exploit it directly without needing to trick another user. Once exploited, the attacker can potentially read sensitive data from protected endpoints, modify system configurations, or escalate their privileges within the Splunk environment.

Detection Methods for CVE-2023-32708

Indicators of Compromise

• Unusual rest SPL command executions containing encoded CRLF sequences (%0d%0a or \r\n)
• Access logs showing requests to REST endpoints from users who should not have permissions
• Anomalous SPL queries with URL-encoded special characters in rest command parameters
• Unexpected API calls to sensitive configuration or authentication endpoints

Detection Strategies

• Monitor Splunk search logs for rest SPL commands containing suspicious character sequences
• Implement detection rules to identify URL-encoded CRLF patterns in SPL queries
• Review audit logs for REST API access patterns that deviate from normal user behavior
• Deploy the Splunk Research detection rule specifically designed for this vulnerability

Monitoring Recommendations

• Enable verbose logging for all rest SPL command executions
• Configure alerts for unusual REST endpoint access patterns from low-privilege accounts
• Implement real-time monitoring of SPL queries for injection attack indicators
• Review Splunk internal logs for HTTP response anomalies or malformed headers

How to Mitigate CVE-2023-32708

Immediate Actions Required

• Upgrade Splunk Enterprise to version 9.0.5, 8.2.11, or 8.1.14 or later depending on your version branch
• Upgrade Splunk Cloud Platform to version 9.0.2303.100 or later
• Review user permissions and restrict access to the rest SPL command where possible
• Audit recent SPL query logs for potential exploitation attempts

Patch Information

Splunk has released security patches addressing this vulnerability in the following versions:

• Splunk Enterprise 9.0.5 and later
• Splunk Enterprise 8.2.11 and later
• Splunk Enterprise 8.1.14 and later
• Splunk Cloud Platform 9.0.2303.100 and later

For detailed patch information and upgrade instructions, refer to the Splunk Security Advisory SVD-2023-0603.

Workarounds

• Restrict the rest SPL command capabilities using role-based access controls until patching is complete
• Implement network segmentation to limit internal REST API exposure
• Use Splunk's capability settings to limit which users can execute the rest command
• Monitor and rate-limit REST API access from authenticated sessions

# Example: Restrict rest command capability in authorize.conf
# Add to $SPLUNK_HOME/etc/system/local/authorize.conf
[role_restricted_user]
# Remove or restrict rest_properties_get and rest_properties_set capabilities
rest_properties_get = disabled
rest_properties_set = disabled