CVE-2025-11539: Grafana Image Renderer RCE Vulnerability

CVE-2025-11539 Overview

CVE-2025-11539 is a critical remote code execution vulnerability affecting Grafana Image Renderer, a plugin service used to render panels and dashboards to PNG images. The vulnerability stems from an arbitrary file write flaw in the /render/csv endpoint, where insufficient validation of the filePath parameter allows attackers to write malicious shared objects to arbitrary locations on the filesystem. These shared objects are subsequently loaded by the Chromium rendering process, leading to remote code execution.

The vulnerability is exploitable when the default authentication token (authToken) has not been changed or is known to the attacker, and when the attacker can reach the image renderer endpoint over the network.

Critical Impact

Successful exploitation enables attackers to achieve remote code execution on systems running vulnerable Grafana Image Renderer instances, potentially leading to complete system compromise, data exfiltration, and lateral movement within affected infrastructure.

Affected Products

• Grafana Image Renderer versions 1.0.0 through 4.0.16
• Systems using default or weak authToken configurations
• Network-accessible Grafana Image Renderer deployments

Discovery Timeline

• 2025-10-09 - CVE-2025-11539 published to NVD
• 2025-10-09 - Last updated in NVD database

Technical Details for CVE-2025-11539

Vulnerability Analysis

This vulnerability is classified as CWE-94 (Improper Control of Generation of Code), which encompasses code injection vulnerabilities where user-controlled input can influence code execution. The attack surface is network-based, requiring only low privileges to exploit, and the scope is changed—meaning a successful exploit can impact resources beyond the vulnerable component's security scope.

The /render/csv endpoint in Grafana Image Renderer accepts a filePath parameter that determines where rendered content is saved. Due to missing or inadequate input validation, an attacker can manipulate this parameter to write files to arbitrary locations on the filesystem. By crafting a malicious shared object (.so file) and writing it to a location where the Chromium browser process loads libraries, the attacker achieves code execution within the context of the rendering service.

Root Cause

The root cause is insufficient input validation on the filePath parameter in the /render/csv endpoint. The application fails to properly sanitize or restrict file paths, allowing directory traversal sequences and arbitrary path specifications. This enables attackers to escape the intended output directory and write files anywhere the application process has write permissions.

Attack Vector

The attack follows a multi-stage exploitation pattern:

1. Authentication Bypass: The attacker must either exploit default credentials (unchanged authToken value) or obtain valid authentication tokens through other means.

2. Malicious Payload Preparation: The attacker crafts a malicious shared object file containing executable code designed to run when loaded by the Chromium process.

3. Arbitrary File Write: Using the vulnerable /render/csv endpoint, the attacker submits a request with a manipulated filePath parameter pointing to a directory where Chromium loads shared libraries.

4. Code Execution Trigger: When Chromium processes subsequent rendering requests, it loads the malicious shared object, executing the attacker's code with the privileges of the rendering service.

The attack can be executed entirely over the network without user interaction, making it particularly dangerous for internet-exposed Grafana deployments.

Detection Methods for CVE-2025-11539

Indicators of Compromise

• Unexpected .so files appearing in Chromium library directories or other sensitive system paths
• Unusual file write operations originating from the Grafana Image Renderer process
• Authentication attempts using the default authToken value against the /render/csv endpoint
• Anomalous outbound network connections from the Chromium or image renderer processes

Detection Strategies

• Monitor HTTP requests to the /render/csv endpoint for suspicious filePath parameters containing path traversal sequences (../) or absolute paths
• Implement file integrity monitoring on directories where Chromium loads shared libraries
• Deploy web application firewall rules to detect and block requests with path traversal patterns targeting Grafana endpoints
• Analyze process creation events for unexpected child processes spawned by the image renderer service

Monitoring Recommendations

• Enable detailed logging for all Grafana Image Renderer API endpoints, particularly authentication events and file operations
• Configure alerting for any file creation events in system library directories attributed to the image renderer process
• Monitor for changes to the authToken configuration and alert on any reversion to default values
• Implement network segmentation monitoring to detect lateral movement attempts from compromised rendering services

How to Mitigate CVE-2025-11539

Immediate Actions Required

• Upgrade Grafana Image Renderer to version 4.0.17 or later immediately
• Change the default authToken to a strong, unique value if not already done
• Restrict network access to the image renderer endpoint using firewall rules or network segmentation
• Audit existing deployments for signs of compromise before patching

Patch Information

Grafana has released version 4.0.17 which addresses this vulnerability by implementing proper input validation on the filePath parameter. The fix prevents directory traversal and restricts file writes to designated output directories. For detailed release information, see the GitHub Release v4.0.17 and the Grafana Security Advisory for CVE-2025-11539.

Workarounds

• If immediate patching is not possible, place the Grafana Image Renderer behind a reverse proxy that blocks requests containing path traversal sequences in the filePath parameter
• Implement strict network access controls to limit which hosts can reach the image renderer endpoint
• Change the authToken from the default value to prevent unauthorized access to the rendering API
• Consider temporarily disabling the image renderer service if it is not critical to operations until patching can be completed

# Configuration example - Change default authToken in Grafana Image Renderer
# Edit the renderer configuration file or set environment variable

# Option 1: Environment variable
export GF_RENDERER_AUTH_TOKEN="your-strong-unique-token-here"

# Option 2: In config file (config.json)
# Set: "authToken": "your-strong-unique-token-here"

# Restrict network access (example iptables rule)
iptables -A INPUT -p tcp --dport 8081 -s trusted_network/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8081 -j DROP