CVE-2021-27358: Grafana Snapshot Feature DoS Vulnerability

CVE-2021-27358 Overview

CVE-2021-27358 is a Denial of Service vulnerability affecting Grafana versions 6.7.3 through 7.4.1. The vulnerability exists in the snapshot feature and can allow unauthenticated remote attackers to trigger a Denial of Service condition via a remote API call when a commonly used configuration is set. This vulnerability poses a significant risk to organizations relying on Grafana for monitoring and observability, as it can disrupt critical dashboard functionality without requiring any authentication.

Critical Impact

Unauthenticated attackers can remotely crash Grafana instances by exploiting the snapshot API endpoint, causing complete loss of monitoring capabilities and potential cascading effects on incident response workflows.

Affected Products

• Grafana versions 6.7.3 through 7.4.1
• NetApp E-Series Performance Analyzer

Discovery Timeline

• 2021-02-17 - Grafana releases security patch in version 7.4.2
• 2021-03-18 - CVE-2021-27358 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-27358

Vulnerability Analysis

This Denial of Service vulnerability resides in Grafana's snapshot feature, which is designed to allow users to capture and share dashboard states. The vulnerability can be triggered remotely through the snapshot API without requiring authentication when Grafana is deployed with certain common configurations. When exploited, an attacker can cause resource exhaustion or service disruption, rendering the Grafana instance unavailable to legitimate users.

The attack exploits improper handling of API requests to the snapshot endpoint, which fails to properly validate or rate-limit incoming requests from unauthenticated sources. This architectural weakness allows malicious actors to overwhelm the service with specially crafted requests.

Root Cause

The root cause stems from insufficient input validation and missing authentication checks in the snapshot API functionality. When Grafana is configured with anonymous access enabled or certain permissive settings (which are common in internal deployments), the snapshot endpoint becomes accessible to unauthenticated users. The lack of proper request validation and rate limiting mechanisms allows attackers to abuse this endpoint to trigger a denial of service condition.

Attack Vector

The attack can be executed remotely over the network without requiring any authentication or user interaction. An attacker simply needs network access to the Grafana instance and knowledge of the snapshot API endpoint. The attack involves sending malicious API calls to the snapshot feature, which when processed, causes the service to become unresponsive or crash entirely.

The vulnerability is particularly dangerous in environments where Grafana is exposed to untrusted networks or where anonymous access is enabled for convenience. Attackers can identify vulnerable instances through network scanning and exploit them without prior knowledge of credentials or internal system details.

Detection Methods for CVE-2021-27358

Indicators of Compromise

• Unusual spike in API requests to the /api/snapshots endpoint from unknown or external IP addresses
• Grafana service crashes or restarts correlating with high volume of snapshot-related requests
• Error logs showing snapshot-related exceptions or resource exhaustion messages
• Network traffic patterns showing repeated connections from single sources to the Grafana API

Detection Strategies

• Monitor Grafana access logs for anomalous patterns targeting the snapshot API endpoint
• Implement alerting on Grafana service availability and unexpected restarts
• Deploy network-based intrusion detection rules to identify DoS attack patterns against Grafana
• Review authentication logs for patterns of unauthenticated access attempts to sensitive API endpoints

Monitoring Recommendations

• Configure application performance monitoring (APM) to track Grafana response times and error rates
• Establish baseline metrics for snapshot API usage to detect deviations indicating potential attacks
• Enable detailed logging for all snapshot-related operations and centralize logs for analysis
• Implement automated alerting when Grafana service becomes unresponsive or experiences high latency

How to Mitigate CVE-2021-27358

Immediate Actions Required

• Upgrade Grafana to version 7.4.2 or later immediately to address this vulnerability
• Review and restrict anonymous access settings in Grafana configuration
• Implement network-level access controls to limit exposure of Grafana instances to trusted networks
• Enable authentication requirements for all API endpoints where possible

Patch Information

Grafana has released version 7.4.2 which addresses this vulnerability. Organizations should upgrade to this version or later as soon as possible. Detailed release notes and changelog information are available through the Grafana Release Notes 7.4.2 and the GitHub Grafana Changelog. NetApp users should also review the NetApp Security Advisory NTAP-20210513-0007 for guidance specific to E-Series Performance Analyzer deployments.

Workarounds

• Disable the snapshot feature entirely if not required for operations by modifying Grafana configuration
• Place Grafana behind a reverse proxy with authentication and rate limiting capabilities
• Implement Web Application Firewall (WAF) rules to block suspicious traffic patterns to the snapshot API
• Restrict network access to Grafana using firewall rules to allow only trusted IP ranges

# Configuration example - Disable anonymous access in grafana.ini
[auth.anonymous]
enabled = false

# Enable authentication for API access
[auth]
disable_login_form = false

# Consider placing behind reverse proxy with rate limiting
# Example nginx rate limiting configuration
# limit_req_zone $binary_remote_addr zone=grafana_api:10m rate=10r/s;