Dangling Dns in Cassandra

Dangling DNS in Cassandra environments typically occurs when DNS records point to decommissioned or non-existent Cassandra nodes, creating attack opportunities that can lead to data exfiltration or service disruption. This manifests in several Cassandra-specific scenarios.

One common pattern is when Cassandra's gossip protocol continues referencing nodes that have been removed from the cluster but whose DNS records weren't cleaned up. Attackers can register these domains and intercept gossip traffic, potentially gaining insights into cluster topology and configuration details.

Cassandra's native transport protocol (CQL) over Thrift or native protocol versions can be vulnerable when DNS records point to decommissioned nodes. An attacker controlling such a domain can intercept CQL connections, potentially capturing authentication attempts or query patterns that reveal sensitive data structure information.

// Vulnerable Cassandra configuration pointing to potentially dangling DNS
contact_points = ['cassandra-node-1.example.com', 'cassandra-node-2.example.com']
port = 9042

Another Cassandra-specific manifestation occurs in multi-datacenter setups where DNS records for cross-datacenter communication aren't properly cleaned up. When a datacenter is decommissioned, lingering DNS records can create pathways for man-in-the-middle attacks between remaining nodes and attacker-controlled endpoints.

Snapshot and backup operations in Cassandra can also be affected. If DNS records for nodes involved in backup operations aren't cleaned up, backup restoration processes might inadvertently communicate with malicious endpoints, potentially exposing sensitive data during the restoration process.

Detecting dangling DNS in Cassandra environments requires a multi-faceted approach that combines network scanning, configuration analysis, and runtime monitoring. The most effective detection combines automated scanning with manual verification.

Network-level detection should focus on Cassandra's specific ports and protocols. A comprehensive scan would check:

# Network scan for Cassandra services
nmap -p 7000,7001,7199,9042,9160 -oA cassandra_scan cassandra-cluster.example.com

For configuration-based detection, analyze Cassandra's configuration files for references to external services and endpoints. The cassandra.yaml file often contains references to seed nodes, RPC addresses, and storage endpoints that may point to decommissioned infrastructure.

# Check for dangling references in cassandra.yaml
sed -n 's/^[[:space:]]*seeds:[[:space:]]*//p' cassandra.yaml | tr ',' '\n' | while read host; do
  if ! nslookup "$host" >/dev/null 2>&1; then
    echo "Potentially dangling DNS: $host"
  fi
done

middleBrick's API security scanner can detect dangling DNS vulnerabilities in Cassandra-related endpoints by testing DNS resolution and response patterns. The scanner identifies when API endpoints reference potentially decommissioned infrastructure and provides specific remediation guidance.

Runtime monitoring is crucial for Cassandra environments. Tools like nodetool and JMX monitoring can reveal when nodes are attempting to communicate with unreachable or suspicious endpoints. Monitoring gossip traffic patterns can also identify when nodes are trying to reach decommissioned peers.

Remediating dangling DNS in Cassandra environments requires both immediate fixes and long-term process improvements. The remediation approach should address both the technical vulnerabilities and the operational processes that allowed them to occur.

Immediate technical remediation involves updating Cassandra's configuration to remove references to decommissioned nodes and ensuring all DNS records are cleaned up. This includes updating the cassandra.yaml file, removing references from configuration management systems, and updating any load balancer configurations.

# Update cassandra.yaml to remove decommissioned nodes
# Before:
seed_provider:
  - class_name: org.apache.cassandra.locator.SimpleSeedProvider
    parameters:
      - seeds: "192.168.1.10,192.168.1.11,192.168.1.12"

# After (remove decommissioned node):
seed_provider:
  - class_name: org.apache.cassandra.locator.SimpleSeedProvider
    parameters:
      - seeds: "192.168.1.10,192.168.1.11"

For Cassandra clusters using multi-region or multi-datacenter setups, implement proper decommissioning procedures that include DNS record cleanup as a mandatory step. This should be documented in your operational runbooks.

Implement network-level controls to prevent unauthorized access to Cassandra services. This includes firewall rules that restrict access to Cassandra ports only from known, trusted networks and implementing mutual TLS authentication for inter-node communication.

# Cassandra security.yaml configuration for mutual TLS
client_encryption_options:
  enabled: true
  optional: false
  keystore: conf/.keystore
  keystore_password: 
  truststore: conf/.truststore
  truststore_password: 
  protocol: TLS
  algorithm: SunX509
  store_type: JKS
  cipher_suites: [TLS_RSA_WITH_AES_128_CBC_SHA, TLS_RSA_WITH_AES_256_CBC_SHA]
  require_client_auth: true

Implement comprehensive monitoring that alerts when nodes attempt to communicate with unexpected endpoints. This can be achieved through custom alerts in your monitoring system that flag when Cassandra nodes try to connect to IP addresses outside your known infrastructure ranges.

Finally, establish automated validation processes that verify DNS records and endpoint availability before allowing Cassandra nodes to join the cluster. This can be implemented through custom node startup scripts that validate all configured endpoints before initializing the Cassandra process.