Quick Summary
Open Memcached Service Without Binding Restriction is a critical network misconfiguration where the Memcached service is exposed on all network interfaces without authentication or access control. This allows unauthorized users to read, modify, or flush cached data and may also expose the server to amplification-based denial-of-service (DDoS) attacks.
Vulnerability Classification
| Field | Value |
|---|---|
| Vulnerability Type | Insecure Service Exposure |
| CWE ID | CWE-306 – Missing Authentication for Critical Function |
| CVE ID | N/A (Configuration Issue) |
| CVSS 4.0 Base Score | 9.0 (Critical) |
| CVSS Vector | AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H |
| OWASP Category | A05:2021 – Security Misconfiguration |
| Attack Surface | External / Internal Network |
Affected Asset / Environment
- Service: Memcached
- Default Port: 11211 (TCP/UDP)
- Platforms: Linux Servers, Cloud Instances, Containers
- Testing Method: Black-box / External Assessment
- Tools Used: Nmap, Netcat, telnet
Description
The assessor observed that the Memcached service is running and bound to all network interfaces (0.0.0.0), making it accessible from external or untrusted networks. Memcached does not provide built-in authentication by default.
During testing, it was possible to connect to the Memcached service and interact with cached data without providing credentials. In addition to data exposure, publicly accessible Memcached services have historically been abused in large-scale UDP amplification attacks.
Because Memcached is typically intended for internal caching between trusted systems, exposing it publicly significantly increases security risk.
Root Cause
The issue occurs due to improper Memcached configuration where the service is bound to all interfaces and no network-level restriction is implemented.
Common root causes include:
- Service bound to 0.0.0.0
- No firewall restrictions on port 11211
- Default configuration used in production
- Lack of secure deployment baseline
- Misconfigured cloud security groups
Business Impact
Exploitation of this vulnerability may allow attackers to retrieve sensitive application data stored in cache, including session tokens, authentication data, or configuration values.
Attackers may also flush the cache, causing service disruption and degraded application performance. In worst-case scenarios, the service may be leveraged for DDoS amplification attacks, potentially causing reputational damage and service outages.
Technical Impact
An attacker can:
- Connect to Memcached without authentication
- Retrieve cached key-value data
- Modify cached entries
- Flush entire cache
- Use UDP amplification for DDoS attacks
This significantly increases both confidentiality and availability risks.
Proof of Concept (PoC)
Step1: Identify Memcached Service
nmap -sV -p 11211 <target-ip>
If port 11211 is open and identified as memcached, proceed to validation.
Step2: Connect Using Telnet
telnet <target-ip> 11211
If connection is successful without authentication prompt, the service is exposed.
Step3: Retrieve Server Statistics
Inside session:
stats
If server statistics are displayed, unauthorized access is confirmed.
Step4: Enumerate Cached Items
stats items
If item information is returned, cached data may be accessible.
Step5: Flush Cache (Authorized Testing Only)
flush_all
If the command executes successfully without authentication, full access is confirmed.
Exploitation Prerequisites
- Network access to port 11211
- Memcached service running
- No binding restriction
- No firewall or IP-based filtering
Remediation
It is recommended that Memcached services be restricted to internal networks only.
Recommended actions:
- Bind Memcached to localhost or internal IP address
- Disable UDP support if not required
- Restrict port 11211 via firewall rules
- Configure secure cloud security group policies
- Avoid exposing Memcached to public internet
- Conduct periodic configuration audits
After applying changes, verify that external connections are blocked.
Detection and Monitoring
- Monitor network traffic to port 11211
- Alert on external connection attempts
- Conduct periodic external exposure scans
- Monitor for abnormal cache flush events