CVE-2023-40592: Splunk Enterprise XSS Vulnerability

CVE-2023-40592 Overview

A reflected cross-site scripting (XSS) vulnerability exists in Splunk Enterprise that allows attackers to craft malicious web requests targeting the /app/search/table web endpoint. This vulnerability (CWE-79) enables the injection of arbitrary client-side scripts that execute in the context of the victim's browser session. When successfully exploited, attackers can leverage this vulnerability to execute arbitrary commands on the Splunk platform instance, potentially compromising the integrity and confidentiality of monitored data.

Critical Impact

Successful exploitation allows attackers to execute arbitrary commands on the Splunk platform instance through reflected XSS, potentially leading to session hijacking, credential theft, or unauthorized access to sensitive security monitoring data.

Affected Products

• Splunk Enterprise versions below 9.1.1
• Splunk Enterprise versions below 9.0.6
• Splunk Enterprise versions below 8.2.12
• Splunk Cloud Platform (specific affected versions detailed in vendor advisory)

Discovery Timeline

• 2023-08-30 - CVE-2023-40592 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-40592

Vulnerability Analysis

This reflected XSS vulnerability resides in the /app/search/table endpoint within the Splunk Enterprise web interface. The vulnerable endpoint fails to properly sanitize user-supplied input before reflecting it back in the HTTP response, allowing attackers to inject malicious JavaScript code that executes in the victim's browser.

The exploitation chain requires user interaction—an authenticated Splunk user must be tricked into clicking a malicious link or visiting an attacker-controlled page. Once triggered, the injected script runs with the full privileges of the victim's Splunk session, enabling attackers to perform actions as that user, including executing commands on the Splunk platform.

Splunk Enterprise serves as a critical security monitoring and SIEM platform in many enterprise environments, making this vulnerability particularly concerning. An attacker who successfully exploits this flaw could access sensitive log data, modify search queries, create persistent access through dashboard modifications, or pivot to other attack vectors within the monitored infrastructure.

Root Cause

The root cause is improper input validation and output encoding (CWE-79) in the /app/search/table web endpoint. User-supplied parameters are not adequately sanitized before being included in the HTML response, allowing specially crafted input containing JavaScript to be reflected and executed in the victim's browser context.

Attack Vector

The attack is network-based and requires user interaction. An attacker crafts a specially constructed URL containing malicious JavaScript payload targeting the vulnerable endpoint. The attack typically proceeds as follows:

1. Attacker identifies the vulnerable /app/search/table endpoint
2. Attacker constructs a malicious URL with XSS payload embedded in request parameters
3. Attacker delivers the malicious URL to authenticated Splunk users via phishing emails, malicious websites, or social engineering
4. When a victim clicks the link while authenticated to Splunk, the malicious script executes
5. The script can then perform actions as the victim, including executing commands on the Splunk platform

The vulnerability allows the attacker to break out of the expected data context and inject executable code. For detailed technical analysis, refer to the Splunk Security Advisory SVD-2023-0801.

Detection Methods for CVE-2023-40592

Indicators of Compromise

• Suspicious HTTP requests to /app/search/table endpoint containing encoded JavaScript or script tags
• Unusual patterns in web access logs showing reflected content with script elements
• Unexpected user session activity following visits to malformed URLs
• Anomalous command execution on Splunk instances correlated with suspicious web requests

Detection Strategies

• Monitor Splunk web access logs for requests to /app/search/table containing suspicious parameters such as <script>, javascript:, onerror=, or other XSS payload indicators
• Implement web application firewall (WAF) rules to detect and block common XSS patterns in requests to Splunk endpoints
• Review Splunk's internal audit logs for unusual administrative actions or command executions that may indicate post-exploitation activity
• Deploy the Splunk detection analytic provided by Splunk's research team

Monitoring Recommendations

• Enable verbose logging for the Splunk web interface to capture detailed request parameters
• Configure alerting for requests containing common XSS payload patterns targeting Splunk web endpoints
• Monitor for unusual patterns of user behavior that may indicate session hijacking, such as simultaneous logins from different IP addresses
• Implement Content Security Policy (CSP) headers where possible to mitigate the impact of successful XSS attacks

How to Mitigate CVE-2023-40592

Immediate Actions Required

• Upgrade Splunk Enterprise to version 9.1.1, 9.0.6, or 8.2.12 or later depending on your deployment branch
• Review Splunk access logs for evidence of exploitation attempts against the /app/search/table endpoint
• Educate users about the risks of clicking untrusted links, especially those pointing to Splunk instance URLs
• Consider implementing network-level controls to restrict access to Splunk web interface from untrusted networks

Patch Information

Splunk has released security updates addressing this vulnerability. Organizations should upgrade to the following patched versions:

• Splunk Enterprise 9.1.x: Upgrade to version 9.1.1 or later
• Splunk Enterprise 9.0.x: Upgrade to version 9.0.6 or later
• Splunk Enterprise 8.2.x: Upgrade to version 8.2.12 or later

For Splunk Cloud Platform customers, Splunk automatically manages updates. Refer to the Splunk Security Advisory SVD-2023-0801 for complete details on affected versions and patch availability.

Workarounds

• Restrict network access to the Splunk web interface to trusted networks and users only
• Implement a reverse proxy or web application firewall (WAF) with XSS filtering capabilities in front of Splunk instances
• Configure browser security headers including Content-Security-Policy (CSP) to limit script execution
• Monitor and audit all access to the Splunk web interface until patches can be applied

# Example: Restrict Splunk web access via iptables to trusted network
iptables -A INPUT -p tcp --dport 8000 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 8000 -j DROP