Dns Cache Poisoning in Cockroachdb

DNS cache poisoning attacks CockroachDB by corrupting the Domain Name System resolution that the database relies on for inter-node communication and client connectivity. CockroachDB nodes use DNS to resolve peer addresses specified in the --join flag during startup and for dynamic membership via the gossip protocol. An attacker who can poison the DNS cache (e.g., via a compromised local resolver or network MITM) can redirect a node's connection attempt to a malicious server under their control.

Consider a typical cluster startup command:

cockroach start --join=db-node-1.example.com:26257,db-node-2.example.com:26257 --cache=25% --max-sql-memory=2GB

When this command executes, CockroachDB's Go runtime calls net.LookupHost to resolve db-node-1.example.com. If an attacker has poisoned the DNS cache to return 10.0.0.99 (their server) instead of the legitimate IP, the new node will establish a gRPC connection to the attacker's endpoint. This enables several exploits:

• Traffic Interception: The attacker can intercept replication traffic, potentially stealing or altering data.
• Cluster Partition: By serving a fake gossip response, the attacker can isolate the node from the legitimate cluster, causing data inconsistency or downtime.
• Credential Harvesting: If the attacker's server mimics CockroachDB's handshake, it may capture TLS certificates or authentication tokens sent by the joining node.

The vulnerability is exacerbated when CockroachDB is deployed with hostnames in configuration files (e.g., --advertise-addr, --http-addr) or when client applications use DNS to connect to the SQL interface (cockroach sql --host=db.example.com). An attacker controlling the DNS resolution for the client can redirect SQL connections to a rogue server, leading to data exfiltration or injection. This maps to OWASP API Security Top 10 item API4:2023 – Unrestricted Resource Consumption when used to flood the cluster with malicious joins, and SSRF when an attacker exploits DNS resolution to probe internal networks.

Detecting DNS cache poisoning vulnerabilities in CockroachDB requires testing whether the system resolves attacker-controlled hostnames in sensitive contexts. middleBrick's SSRF (Server-Side Request Forgery) check probes for this by submitting a URL parameter that triggers a DNS lookup and observing if the system initiates a connection to a domain under the scanner's control. For CockroachDB's HTTP-based admin interface (port 8080), the scanner tests endpoints that may accept hostnames, such as node addition APIs (if exposed) or debug endpoints that perform external lookups.

Example scan command and interpretation:

middlebrick scan https://cockroachdb-admin.example.com:8080

The scanner's report might include a finding like:

While CockroachDB's core node join process is not typically exposed via HTTP API, misconfigurations (e.g., enabling debug endpoints in production) or custom extensions could create attack surfaces. middleBrick also correlates this with its Inventory Management check: if the scanner discovers that the cluster advertises internal hostnames (e.g., cockroachdb-internal) that resolve to private IPs, it flags potential DNS takeover risks. The OpenAPI/Swagger spec analysis feature can identify parameters typed as string with format: hostname that might be used in DNS-sensitive operations.

Remediation focuses on eliminating DNS reliance for critical operations and securing the resolution chain. CockroachDB provides native features to bypass DNS entirely:

1. Use IP Addresses in --join and --advertise-addr: Replace all hostnames with static IPs. This is the most effective fix, as it removes DNS from the node discovery path.

# Insecure (vulnerable to DNS poisoning)
cockroach start --join=db-node-1.example.com:26257,db-node-2.example.com:26257

# Secure (uses IPs)
cockroach start --join=10.1.2.3:26257,10.1.2.4:26257 --advertise-addr=10.1.2.3

2. Enforce mTLS for Node Communication: Even if DNS is poisoned, mutual TLS prevents an attacker from decrypting or tampering with traffic. Generate certificates and start nodes with:

   cockroach start --certs-dir=/certs --join=10.1.2.3:26257,10.1.2.4:26257 --cluster-secure

3. Configure Static DNS Resolution for the OS: On each node, edit /etc/resolv.conf (Linux) or network settings to use only trusted, internal DNS servers that validate responses via DNSSEC. Avoid public resolvers for internal hostnames.
4. Disable Unnecessary Debug Endpoints: Ensure the admin UI (port 8080) is firewalled from the public internet. In cockroach start, omit --http-addr if not needed, or bind it to 127.0.0.1.

For client applications, use IP addresses in connection strings. If hostnames are unavoidable (e.g., in cloud environments with dynamic IPs), implement DNS pinning in the application layer or use a service mesh (like Istio) that provides its own secure service discovery. CockroachDB's --dns-srv flag (for Kubernetes deployments) should be used only with a secured, cluster-managed DNS service like CoreDNS with DNSSEC enabled.