Arp Spoofing in Redis

ARP spoofing is a layer-2 network attack where an attacker sends forged ARP messages onto a local area network, linking their MAC address with the IP address of a legitimate server (like a Redis instance). This enables a man-in-the-middle (MITM) position, allowing the attacker to intercept, modify, or drop traffic between clients and the Redis server. While Redis operates at the application layer over TCP, its security is fundamentally undermined if the underlying network segment is compromised via ARP poisoning.

The attack specifically manifests in Redis environments under these conditions:

• Unencrypted Redis on a Shared Network: If Redis is configured to listen on a non-loopback interface (e.g., bind 0.0.0.0 or a specific internal IP) without TLS, all commands, including AUTH credentials and sensitive data (e.g., SET user:123 "secret"), are transmitted in plaintext. An ARP spoofing attacker on the same broadcast domain can capture this traffic using tools like Wireshark or arpspoof, leading to credential theft and data exposure.
• Redis Cluster or Replication Traffic: Redis Cluster uses a gossip protocol and data sharding across nodes. Replication streams from master to replica are also sent in plaintext by default. An ARP attacker positioned between cluster nodes or between a master and its replicas can intercept replication traffic, potentially altering data streams or stealing full dataset snapshots.
• Redis over UNIX Socket: While UNIX domain sockets (unixsocket in redis.conf) are immune to ARP spoofing (as they don't use IP), many deployments expose both a TCP port and a UNIX socket for local and remote access. If the TCP port is enabled without TLS on a shared network, the ARP vulnerability exists for any remote client connecting via that interface.
• Client-Side Vulnerabilities: Applications connecting to Redis from within the same vulnerable network (e.g., a microservice in a Kubernetes pod on an overlay network with misconfigured network policies) can have their Redis traffic intercepted. This is particularly dangerous for internal APIs that use Redis as a session store or cache, as session tokens or cached API responses can be harvested.

A concrete attack scenario: An attacker gains access to a corporate Wi-Fi or a compromised VM in the same cloud VPC. They execute arpspoof -i eth0 -t <redis-server-ip> <gateway-ip> to poison the ARP cache of the Redis server and the default gateway. All Redis traffic from application servers now flows through the attacker's machine. If Redis uses plaintext TCP, the attacker runs tcpdump -i eth0 port 6379 -w redis.pcap to capture credentials and data, later extracting the AUTH password from the packet payload using strings or a custom parser.

middleBrick detects configurations that make Redis endpoints vulnerable to ARP spoofing by identifying the absence of encryption and improper network binding during its unauthenticated black-box scan. The scanner does not detect active ARP poisoning on the network (a network-layer forensic task), but it flags the precondition: an exposed Redis instance that transmits sensitive data in plaintext.

During a scan of a Redis endpoint (e.g., http://api.example.com/redis or a direct Redis URI if supported), middleBrick performs these relevant checks:

• Encryption Check: It attempts a TLS handshake. If the server responds on the default Redis port (6379) or a custom port without TLS negotiation, the check fails. The scanner also inspects the Redis INFO command response (if unauthenticated access is possible) for the tls_port configuration flag. Absence of TLS indicates that all traffic, including authentication, is clear-text.
• Data Exposure Check: If the scanner can issue commands (due to no AUTH or weak authentication), it probes for sensitive key patterns (e.g., keys user:*, get session:*) and flags any accessible data. Even without command execution, the mere exposure of the Redis port without TLS is a critical finding because it enables ARP spoofing to steal credentials.
• Authentication Check: middleBrick tests for the presence of the AUTH password requirement. If Redis is configured with protected-mode no and bind 0.0.0.0 without a password, it is publicly accessible. However, even with a password, if TLS is absent, the password is sent in plaintext, making it vulnerable to ARP-based credential harvesting.

For example, scanning a misconfigured Redis instance yields a report with:

middleBrick's OpenAPI/Swagger analysis can also flag if an API specification documents a Redis backend with connection strings using redis:// (unencrypted) instead of rediss:// (TLS), providing a cross-reference between design and runtime exposure.

To use middleBrick for this detection:

# CLI scan of a Redis endpoint (if exposed via HTTP wrapper or direct TCP scan support)
middlebrick scan redis://redis.example.com:6379

# Or scan the API that uses Redis as a backend
middlebrick scan https://api.example.com/v1

The resulting score will be downgraded due to the encryption failure, and the remediation guidance will explicitly mention ARP spoofing as a threat enabled by unencrypted traffic.

Remediation focuses on encrypting Redis traffic and restricting network exposure. middleBrick provides actionable guidance, but the fixes must be implemented by the Redis administrator or developer using Redis's native features.

1. Enable TLS in Redis Configuration

Redis Open Source and Redis Stack support TLS natively. Edit redis.conf:

# Enable TLS
port 0
tls-port 6379

# Provide certificate and key (generated via OpenSSL)
tls-cert-file /etc/redis/tls/redis.crt
tls-key-file /etc/redis/tls/redis.key

# Optional: require client certificates for mutual TLS
tls-auth-clients no

# Set TLS versions and ciphers (use secure defaults)
tls-version-min TLSv1.2
tls-ciphers HIGH:!aNULL:!MD5

Restart Redis. Clients must now connect using TLS. For example, in Python with redis-py:

import redis

r = redis.Redis(
    host='redis.example.com',
    port=6379,
    ssl=True,
    ssl_cert_reqs='required',  # Verify server certificate
    ssl_ca_certs='/path/to/ca.crt'
)
r.ping()  # Connection now encrypted

2. Bind to Localhost or Internal Interfaces

If Redis is only used locally (e.g., by a web app on the same host), bind to 127.0.0.1:

bind 127.0.0.1
protected-mode yes  # Default, rejects external connections without AUTH

For internal-only access in a VPC, bind to the private IP and use security groups to restrict source IPs.

3. Use Network-Level Encryption (Alternative)

If native Redis TLS is not feasible (older versions), use a stunnel proxy:

# stunnel.conf
client = no
[socket]
accept = 6379
connect = 127.0.0.1:6380  # Redis listening on 6380 without TLS

Clients connect to stunnel on 6379 with TLS; stunnel forwards to Redis on 6380.

4. Enforce Mutual Authentication

For high-security environments, require client certificates:

tls-auth-clients yes
tls-client-cert-file /etc/redis/tls/ca.crt  # CA that signed client certs

5. Rotate Passwords and Use Strong Auth

Even with TLS, use a strong requirepass (or ACLs in Redis 6+). Rotate passwords periodically. Example ACL configuration:

# In redis.conf or via ACL SETUSER
user default on ><hashed_password> ~* +@all

6. Monitor and Alert

Use Redis's SLOWLOG and MONITOR (carefully, in production) to detect unusual command patterns. middleBrick's Pro plan with continuous monitoring can track configuration drift—e.g., if tls-port is removed in a deployment.

Important: middleBrick only reports the vulnerability and suggests these steps. It does not modify Redis configurations. After applying fixes, re-scan with middleBrick to confirm the Encryption check passes and the overall risk score improves.