Dangling Dns in Buffalo with Cockroachdb

A dangling DNS record in a Buffalo application that uses CockroachDB can expose internal hostnames or external endpoints, enabling an attacker to infer infrastructure or redirect traffic. When Buffalo serves dynamic configuration derived from DNS lookups—such as service discovery for a CockroachDB cluster—stale or orphaned DNS entries may resolve to unexpected hosts. Because CockroachDB typically requires long-lived, reliable connections, the application might cache or reuse an address that later points to an unintended service. This mismatch can expose administrative interfaces, allow SSRF against internal endpoints, or facilitate database connection manipulation. The combination of Buffalo’s rapid request handling, CockroachDB’s connection patterns, and unvalidated DNS data increases the likelihood that a client-facing request triggers behavior dependent on a rogue DNS resolution path.

During an unauthenticated scan with middleBrick, this surface is tested by first resolving hostnames observed in configuration or error messages, then attempting to induce the application to perform a lookup or re-resolution. If the application uses net.LookupHost or similar calls to derive CockroachDB node addresses at runtime, middleBrick can supply controlled DNS responses that reveal whether stale records are used. Findings may highlight that a hostname such as cockroach-internal.old-tenant.example.com remains resolvable and is still referenced by the application, even though the corresponding infrastructure has been decommissioned. Because middleBrick’s checks include input validation and SSRF, it flags this as a potential data exposure or SSRF risk when the resolved address leads to an unexpected network service. The scan does not modify DNS or network state; it documents the observable behavior and provides remediation guidance.

In a real-world scenario, consider a Buffalo app that builds a CockroachDB connection string from a service name resolved via DNS. If the DNS entry for that service is not cleaned up during infrastructure rotation, the app may unknowingly connect to a different tenant’s cluster or an external test environment. middleBrick’s OpenAPI/Swagger analysis can correlate spec-defined parameters with runtime DNS behavior, especially when endpoints accept hostnames as input. Cross-referencing the spec with active probes helps determine whether user-supplied values influence DNS resolution in an unsafe way. This illustrates why DNS hygiene must be part of API security hygiene, and why scanning tools that detect such dangling references—like middleBrick, which can be run via its CLI (middlebrick scan <url>) or integrated into CI/CD with the GitHub Action—are valuable for identifying configuration drift before it is abused.

Remediation focuses on ensuring that DNS-derived addresses are validated, pinned, or explicitly managed so that Buffalo does not inadvertently rely on stale records. When constructing connection strings for CockroachDB, prefer static configuration or environment variables that are injected at deploy time, rather than runtime DNS lookups. If dynamic resolution is required, implement strict validation of resolved addresses against an allowlist and avoid caching results across requests. The following code examples demonstrate safer patterns in a Buffalo application.

First, use environment variables for connection parameters and validate them at startup. This avoids runtime DNS lookups for sensitive database endpoints:

// config.go
package app

import (
    "os"
    "net/url"
)

type DBConfig struct {
    Host     string
    Port     string
    User     string
    Password string
    Database string
}

func LoadDBConfig() (*DBConfig, error) {
    host := os.Getenv("COCKROACH_HOST")
    port := os.Getenv("COCKROACH_PORT")
    user := os.Getenv("COCKROACH_USER")
    password := os.Getenv("COCKROACH_PASSWORD")
    database := os.Getenv("COCKROACH_DATABASE")
    if host == "" || port == "" || user == "" || database == "" {
        return nil, ErrMissingEnv
    }
    return &DBConfig{
        Host: host, Port: port, User: user,
        Password: password, Database: database,
    }, nil
}

Second, if you must perform a DNS lookup, resolve once, validate against a known fingerprint or allowlist, and do not reuse the result for unrelated services. The example below resolves a hostname once, checks that it belongs to an expected CIDR range, and returns an error if validation fails:

// dns_validate.go
package app

import (
    "context"
    "net"
    "errors"
)

var allowedCIDR = "192.168.1.0/24" // adjust to your infrastructure

func ResolveAndValidate(ctx context.Context, name string) (string, error) {
    ips, err := net.LookupHost(name)
    if err != nil {
        return "", err
    }
    for _, ip := range ips {
        if ipInAllowedRange(ip) {
            return ip, nil
        }
    }
    return "", errors.New("no valid address found")
}

func ipInAllowedRange(ipStr string) bool {
    _, cidr, _ := net.ParseCIDR(allowedCIDR)
    parsedIP := net.ParseIP(ipStr)
    return cidr.Contains(parsedIP)
}

Third, ensure that any user-supplied input that could affect connection parameters is sanitized and does not directly become a hostname for CockroachDB. Use strict allowlists for characters and length, and avoid concatenating user input into DNS names. These practices reduce the risk that dangling or malicious DNS records can be leveraged via the Buffalo application. By combining configuration discipline with explicit validation, you align the runtime behavior of Buffalo with the security expectations of CockroachDB deployments.