CVE-2025-20371: Splunk Enterprise SSRF Vulnerability

CVE-2025-20371 Overview

CVE-2025-20371 is a blind Server-Side Request Forgery (SSRF) vulnerability affecting Splunk Enterprise and Splunk Cloud Platform. This vulnerability allows an unauthenticated attacker to manipulate server-side requests, potentially enabling them to perform REST API calls on behalf of an authenticated high-privileged user. The blind nature of this SSRF means attackers cannot directly observe the responses, but can still leverage the vulnerability to interact with internal services and APIs.

Critical Impact

Unauthenticated attackers can trigger blind SSRF to execute REST API calls with high-privileged user permissions, potentially leading to unauthorized data access, configuration changes, or further exploitation of internal systems.

Affected Products

• Splunk Enterprise versions below 10.0.1, 9.4.4, 9.3.6, and 9.2.8
• Splunk Enterprise version 10.0.0
• Splunk Cloud Platform versions below 9.3.2411.109, 9.3.2408.119, and 9.2.2406.122

Discovery Timeline

• 2025-10-01 - CVE-2025-20371 published to NVD
• 2025-10-08 - Last updated in NVD database

Technical Details for CVE-2025-20371

Vulnerability Analysis

This vulnerability is classified under CWE-918 (Server-Side Request Forgery), which occurs when an application fetches remote resources based on user-supplied input without properly validating the destination URL. In the context of Splunk Enterprise and Cloud Platform, an unauthenticated attacker can craft malicious requests that cause the Splunk server to make HTTP requests to arbitrary destinations.

The blind SSRF variant is particularly dangerous because it allows attackers to probe internal network infrastructure, access internal services that are not directly exposed to the internet, and potentially execute privileged REST API calls. Since the vulnerability requires no prior authentication, the attack surface is significantly broadened, making it accessible to any network-level attacker who can reach the Splunk instance.

The impact of successful exploitation includes the ability to interact with internal REST API endpoints as if the request originated from a high-privileged authenticated user. This could lead to unauthorized configuration changes, data exfiltration, or pivoting to other internal systems.

Root Cause

The root cause of this vulnerability lies in insufficient validation of user-controlled input that is subsequently used in server-side HTTP requests. The Splunk application fails to properly sanitize or restrict the destination URLs when processing certain requests, allowing attackers to redirect server-side requests to arbitrary internal or external endpoints. This lack of input validation combined with the absence of authentication requirements for the affected functionality creates a significant security gap.

Attack Vector

The attack is network-based and requires user interaction. An attacker must craft a malicious request and entice an authenticated high-privileged user to trigger the vulnerable functionality. The attack flow involves the following sequence:

1. The attacker identifies the vulnerable endpoint in the Splunk application
2. A crafted request is created that contains a malicious URL destination
3. When processed by the Splunk server, the application makes an HTTP request to the attacker-controlled or internal destination
4. The server-side request is executed with the privileges of an authenticated high-privileged user
5. While the attacker cannot directly see the response (blind SSRF), they can infer information through timing, error conditions, or out-of-band channels

The vulnerability allows attackers to target internal services, cloud metadata endpoints, and other sensitive resources that would normally be inaccessible from external networks.

Detection Methods for CVE-2025-20371

Indicators of Compromise

• Unusual outbound HTTP/HTTPS requests from Splunk servers to internal IP ranges or unexpected external destinations
• Server-side requests to cloud metadata endpoints (e.g., 169.254.169.254)
• Unexpected REST API activity or configuration changes performed by service accounts
• Log entries showing requests with suspicious URL parameters targeting internal network resources

Detection Strategies

• Monitor Splunk server network traffic for anomalous outbound connections to internal services or metadata endpoints
• Implement network segmentation monitoring to detect lateral movement attempts originating from Splunk servers
• Analyze Splunk audit logs for REST API calls that do not correlate with expected user sessions
• Deploy web application firewall (WAF) rules to detect and block SSRF attack patterns in incoming requests
• Review authentication logs for privilege escalation indicators following SSRF-like activity

Monitoring Recommendations

• Enable verbose logging on Splunk instances to capture detailed request information
• Configure alerts for outbound connections from Splunk servers to internal network ranges
• Monitor for DNS queries from Splunk servers to unexpected or suspicious domains
• Implement egress filtering and logging to detect potential data exfiltration attempts

How to Mitigate CVE-2025-20371

Immediate Actions Required

• Upgrade Splunk Enterprise to version 10.0.1, 9.4.4, 9.3.6, or 9.2.8 or later depending on your current version branch
• Upgrade Splunk Cloud Platform to version 9.3.2411.109, 9.3.2408.119, or 9.2.2406.122 or later
• Implement network-level controls to restrict Splunk server outbound connections
• Review and audit recent REST API activity for any signs of unauthorized access

Patch Information

Splunk has released security patches addressing this vulnerability. Detailed patch information and upgrade instructions are available in the Splunk Security Advisory SVD-2025-1006. Organizations should prioritize patching based on the severity of this vulnerability and the exposure of their Splunk deployments.

For Splunk Enterprise deployments, ensure you upgrade to the following minimum versions:

• Branch 10.0.x: Upgrade to 10.0.1 or later
• Branch 9.4.x: Upgrade to 9.4.4 or later
• Branch 9.3.x: Upgrade to 9.3.6 or later
• Branch 9.2.x: Upgrade to 9.2.8 or later

Workarounds

• Implement strict network segmentation to limit Splunk server access to only required internal resources
• Deploy a web application firewall (WAF) with SSRF detection rules in front of Splunk instances
• Configure egress firewall rules to block Splunk servers from initiating connections to sensitive internal endpoints
• Restrict access to the Splunk web interface to trusted networks only until patches can be applied

# Example iptables rule to restrict Splunk server outbound connections
# Block outbound connections to internal network ranges from Splunk server
iptables -A OUTPUT -p tcp -d 10.0.0.0/8 -j DROP
iptables -A OUTPUT -p tcp -d 172.16.0.0/12 -j DROP
iptables -A OUTPUT -p tcp -d 192.168.0.0/16 -j DROP
# Allow necessary outbound connections (customize as needed)
iptables -A OUTPUT -p tcp --dport 443 -d <allowed_destination> -j ACCEPT